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 $62.78   6.572%   $66.9059   $66.91   $66.90   $66.90  
  Purchase #2 $176.45   4.257%   $183.9615   $183.96   $183.95   $184.00  
  Purchase #3 $108.77   12.855%   $122.7524   $122.75   $122.75   $122.80  
  Purchase #4 $89.37   8.590%   $97.0469   $97.05   $97.05   $97.00  
  Purchase #5 $119.94   6.785%   $128.0779   $128.08   $128.10   $128.10  
  Purchase #6 $191.85   11.324%   $213.5751   $213.58   $213.60   $213.60  
  Purchase #7 $162.91   4.833%   $170.7834   $170.78   $170.80   $170.80  
  7 purchase totals = $912.07       $983.1031   $983.11   $983.15   $983.20