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 $178.39   8.466%   $193.4925   $193.49   $193.50   $193.50  
  Purchase #2 $119.28   5.583%   $125.9394   $125.94   $125.95   $125.90  
  Purchase #3 $166.93   11.135%   $185.5177   $185.52   $185.50   $185.50  
  Purchase #4 $238.54   5.510%   $251.6836   $251.68   $251.70   $251.70  
  Purchase #5 $241.44   10.220%   $266.1152   $266.12   $266.10   $266.10  
  Purchase #6 $123.70   9.557%   $135.522   $135.52   $135.50   $135.50  
  Purchase #7 $207.35   9.756%   $227.5791   $227.58   $227.60   $227.60  
  7 purchase totals = $1,275.63       $1,385.8495   $1,385.85   $1,385.85   $1,385.80