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 $94.48   12.207%   $106.0132   $106.01   $106.00   $106.00  
  Purchase #2 $221.52   6.834%   $236.6587   $236.66   $236.65   $236.70  
  Purchase #3 $197.73   8.677%   $214.887   $214.89   $214.90   $214.90  
  Purchase #4 $45.40   7.444%   $48.7796   $48.78   $48.80   $48.80  
  Purchase #5 $69.44   11.545%   $77.4568   $77.46   $77.45   $77.50  
  Purchase #6 $232.57   7.209%   $249.336   $249.34   $249.35   $249.30  
  Purchase #7 $48.32   6.382%   $51.4038   $51.40   $51.40   $51.40  
  7 purchase totals = $909.46       $984.5351   $984.54   $984.55   $984.60