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 $33.77   8.444%   $36.6215   $36.62   $36.60   $36.60  
  Purchase #2 $41.59   11.431%   $46.3442   $46.34   $46.35   $46.30  
  Purchase #3 $50.46   5.189%   $53.0784   $53.08   $53.10   $53.10  
  Purchase #4 $175.75   3.594%   $182.0665   $182.07   $182.05   $182.10  
  Purchase #5 $110.55   5.149%   $116.2422   $116.24   $116.25   $116.20  
  Purchase #6 $54.89   13.861%   $62.4983   $62.50   $62.50   $62.50  
  Purchase #7 $185.60   10.267%   $204.6556   $204.66   $204.65   $204.70  
  7 purchase totals = $652.61       $701.5067   $701.51   $701.50   $701.50