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 $84.32   10.592%   $93.2512   $93.25   $93.25   $93.30  
  Purchase #2 $15.75   7.567%   $16.9418   $16.94   $16.95   $16.90  
  Purchase #3 $13.54   4.144%   $14.1011   $14.10   $14.10   $14.10  
  Purchase #4 $106.95   6.340%   $113.7306   $113.73   $113.75   $113.70  
  Purchase #5 $233.65   8.862%   $254.3561   $254.36   $254.35   $254.40  
  Purchase #6 $201.26   11.109%   $223.618   $223.62   $223.60   $223.60  
  Purchase #7 $235.65   10.316%   $259.9597   $259.96   $259.95   $260.00  
  7 purchase totals = $891.12       $975.9585   $975.96   $975.95   $976.00