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 $82.95   12.498%   $93.3171   $93.32   $93.30   $93.30  
  Purchase #2 $224.95   6.695%   $240.0104   $240.01   $240.00   $240.00  
  Purchase #3 $22.31   7.387%   $23.958   $23.96   $23.95   $24.00  
  Purchase #4 $78.98   13.552%   $89.6834   $89.68   $89.70   $89.70  
  Purchase #5 $75.35   13.453%   $85.4868   $85.49   $85.50   $85.50  
  Purchase #6 $169.82   13.820%   $193.2891   $193.29   $193.30   $193.30  
  Purchase #7 $31.75   6.126%   $33.695   $33.70   $33.70   $33.70  
  7 purchase totals = $686.11       $759.4398   $759.45   $759.45   $759.50