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 $62.46   5.837%   $66.1058   $66.11   $66.10   $66.10  
  Purchase #2 $153.79   6.816%   $164.2723   $164.27   $164.25   $164.30  
  Purchase #3 $197.58   4.132%   $205.744   $205.74   $205.75   $205.70  
  Purchase #4 $204.72   12.208%   $229.7122   $229.71   $229.70   $229.70  
  Purchase #5 $8.88   10.327%   $9.797   $9.80   $9.80   $9.80  
  Purchase #6 $191.43   9.475%   $209.568   $209.57   $209.55   $209.60  
  Purchase #7 $155.66   13.519%   $176.7037   $176.70   $176.70   $176.70  
  7 purchase totals = $974.52       $1,061.9030   $1,061.90   $1,061.85   $1,061.90