Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $108.45   10.205%   $119.5173   $119.52   $119.50   $119.50  
  Purchase #2 $170.47   13.590%   $193.6369   $193.64   $193.65   $193.60  
  Purchase #3 $111.68   6.777%   $119.2486   $119.25   $119.25   $119.20  
  Purchase #4 $250.88   6.739%   $267.7868   $267.79   $267.80   $267.80  
  Purchase #5 $213.94   13.201%   $242.1822   $242.18   $242.20   $242.20  
  Purchase #6 $107.76   4.671%   $112.7935   $112.79   $112.80   $112.80  
  Purchase #7 $154.98   8.770%   $168.5717   $168.57   $168.55   $168.60  
  7 purchase totals = $1,118.16       $1,223.7370   $1,223.74   $1,223.75   $1,223.70