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 $56.63   10.466%   $62.5569   $62.56   $62.55   $62.60  
  Purchase #2 $247.63   8.427%   $268.4978   $268.50   $268.50   $268.50  
  Purchase #3 $53.77   9.191%   $58.712   $58.71   $58.70   $58.70  
  Purchase #4 $156.75   11.595%   $174.9252   $174.93   $174.95   $174.90  
  Purchase #5 $52.57   9.192%   $57.4022   $57.40   $57.40   $57.40  
  Purchase #6 $99.82   6.492%   $106.3003   $106.30   $106.30   $106.30  
  Purchase #7 $101.32   7.196%   $108.611   $108.61   $108.60   $108.60  
  7 purchase totals = $768.49       $837.0054   $837.01   $837.00   $837.00