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 $59.80   6.868%   $63.9071   $63.91   $63.90   $63.90  
  Purchase #2 $113.83   7.701%   $122.596   $122.60   $122.60   $122.60  
  Purchase #3 $78.32   11.626%   $87.4255   $87.43   $87.45   $87.40  
  Purchase #4 $58.55   10.261%   $64.5578   $64.56   $64.55   $64.60  
  Purchase #5 $110.34   7.226%   $118.3132   $118.31   $118.30   $118.30  
  Purchase #6 $165.41   11.394%   $184.2568   $184.26   $184.25   $184.30  
  Purchase #7 $187.89   7.497%   $201.9761   $201.98   $202.00   $202.00  
  7 purchase totals = $774.14       $843.0325   $843.05   $843.05   $843.10