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 $22.66   6.122%   $24.0472   $24.05   $24.05   $24.00  
  Purchase #2 $152.93   3.237%   $157.8803   $157.88   $157.90   $157.90  
  Purchase #3 $116.71   12.512%   $131.3128   $131.31   $131.30   $131.30  
  Purchase #4 $32.91   7.332%   $35.323   $35.32   $35.30   $35.30  
  Purchase #5 $173.99   13.722%   $197.8649   $197.86   $197.85   $197.90  
  Purchase #6 $78.64   11.399%   $87.6042   $87.60   $87.60   $87.60  
  Purchase #7 $207.32   12.375%   $232.9759   $232.98   $233.00   $233.00  
  7 purchase totals = $785.16       $867.0083   $867.00   $867.00   $867.00