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 $189.69   9.131%   $207.0106   $207.01   $207.00   $207.00  
  Purchase #2 $183.54   11.732%   $205.0729   $205.07   $205.05   $205.10  
  Purchase #3 $215.68   10.535%   $238.4019   $238.40   $238.40   $238.40  
  Purchase #4 $73.29   3.186%   $75.625   $75.63   $75.65   $75.60  
  Purchase #5 $41.32   13.361%   $46.8408   $46.84   $46.85   $46.80  
  Purchase #6 $33.94   6.664%   $36.2018   $36.20   $36.20   $36.20  
  Purchase #7 $60.37   10.307%   $66.5923   $66.59   $66.60   $66.60  
  7 purchase totals = $797.83       $875.7453   $875.74   $875.75   $875.70