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 $65.88   12.362%   $74.0241   $74.02   $74.00   $74.00  
  Purchase #2 $59.71   10.205%   $65.8034   $65.80   $65.80   $65.80  
  Purchase #3 $80.96   12.610%   $91.1691   $91.17   $91.15   $91.20  
  Purchase #4 $14.99   8.519%   $16.267   $16.27   $16.25   $16.30  
  Purchase #5 $77.78   11.710%   $86.888   $86.89   $86.90   $86.90  
  Purchase #6 $158.94   9.487%   $174.0186   $174.02   $174.00   $174.00  
  Purchase #7 $185.81   8.754%   $202.0758   $202.08   $202.10   $202.10  
  7 purchase totals = $644.07       $710.2460   $710.25   $710.20   $710.30