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 $187.88   9.605%   $205.9259   $205.93   $205.95   $205.90  
  Purchase #2 $46.86   13.256%   $53.0718   $53.07   $53.05   $53.10  
  Purchase #3 $56.49   7.230%   $60.5742   $60.57   $60.55   $60.60  
  Purchase #4 $217.99   7.781%   $234.9518   $234.95   $234.95   $235.00  
  Purchase #5 $97.91   10.511%   $108.2013   $108.20   $108.20   $108.20  
  Purchase #6 $83.50   12.691%   $94.097   $94.10   $94.10   $94.10  
  Purchase #7 $63.70   5.130%   $66.9678   $66.97   $66.95   $67.00  
  7 purchase totals = $754.33       $823.7898   $823.79   $823.75   $823.90