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 $188.79   3.281%   $194.9842   $194.98   $195.00   $195.00  
  Purchase #2 $177.68   12.679%   $200.208   $200.21   $200.20   $200.20  
  Purchase #3 $32.31   7.610%   $34.7688   $34.77   $34.75   $34.80  
  Purchase #4 $183.90   9.319%   $201.0376   $201.04   $201.05   $201.00  
  Purchase #5 $128.55   9.601%   $140.8921   $140.89   $140.90   $140.90  
  Purchase #6 $23.88   7.864%   $25.7579   $25.76   $25.75   $25.80  
  Purchase #7 $57.69   9.186%   $62.9894   $62.99   $63.00   $63.00  
  7 purchase totals = $792.80       $860.6380   $860.64   $860.65   $860.70