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 $244.43   10.230%   $269.4352   $269.44   $269.45   $269.40  
  Purchase #2 $182.93   4.112%   $190.4521   $190.45   $190.45   $190.50  
  Purchase #3 $223.58   5.821%   $236.5946   $236.59   $236.60   $236.60  
  Purchase #4 $66.71   11.617%   $74.4597   $74.46   $74.45   $74.50  
  Purchase #5 $26.62   6.476%   $28.3439   $28.34   $28.35   $28.30  
  Purchase #6 $87.74   4.801%   $91.9524   $91.95   $91.95   $92.00  
  Purchase #7 $87.34   9.842%   $95.936   $95.94   $95.95   $95.90  
  7 purchase totals = $919.35       $987.1739   $987.17   $987.20   $987.20