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 $132.96   13.819%   $151.3337   $151.33   $151.35   $151.30  
  Purchase #2 $97.68   13.326%   $110.6968   $110.70   $110.70   $110.70  
  Purchase #3 $34.79   8.408%   $37.7151   $37.72   $37.70   $37.70  
  Purchase #4 $192.70   10.563%   $213.0549   $213.05   $213.05   $213.10  
  Purchase #5 $229.88   5.609%   $242.774   $242.77   $242.75   $242.80  
  Purchase #6 $37.94   12.653%   $42.7405   $42.74   $42.75   $42.70  
  Purchase #7 $107.90   9.827%   $118.5033   $118.50   $118.50   $118.50  
  7 purchase totals = $833.85       $916.8183   $916.81   $916.80   $916.80