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 $30.92   7.163%   $33.1348   $33.13   $33.15   $33.10  
  Purchase #2 $221.86   6.810%   $236.9687   $236.97   $236.95   $237.00  
  Purchase #3 $220.83   11.820%   $246.9321   $246.93   $246.95   $246.90  
  Purchase #4 $36.97   4.806%   $38.7468   $38.75   $38.75   $38.70  
  Purchase #5 $49.28   12.860%   $55.6174   $55.62   $55.60   $55.60  
  Purchase #6 $183.99   3.387%   $190.2217   $190.22   $190.20   $190.20  
  Purchase #7 $197.78   11.762%   $221.0429   $221.04   $221.05   $221.00  
  7 purchase totals = $941.63       $1,022.6644   $1,022.66   $1,022.65   $1,022.50