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 $190.75   13.397%   $216.3048   $216.30   $216.30   $216.30  
  Purchase #2 $87.43   7.299%   $93.8115   $93.81   $93.80   $93.80  
  Purchase #3 $58.87   7.508%   $63.29   $63.29   $63.30   $63.30  
  Purchase #4 $132.49   11.572%   $147.8217   $147.82   $147.80   $147.80  
  Purchase #5 $206.96   11.380%   $230.512   $230.51   $230.50   $230.50  
  Purchase #6 $154.76   6.803%   $165.2883   $165.29   $165.30   $165.30  
  Purchase #7 $32.40   3.318%   $33.475   $33.48   $33.50   $33.50  
  7 purchase totals = $863.66       $950.5033   $950.50   $950.50   $950.50