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 $217.79   13.306%   $246.7691   $246.77   $246.75   $246.80  
  Purchase #2 $221.71   11.200%   $246.5415   $246.54   $246.55   $246.50  
  Purchase #3 $210.59   12.674%   $237.2802   $237.28   $237.30   $237.30  
  Purchase #4 $152.90   11.259%   $170.115   $170.12   $170.10   $170.10  
  Purchase #5 $32.73   7.854%   $35.3006   $35.30   $35.30   $35.30  
  Purchase #6 $134.28   7.864%   $144.8398   $144.84   $144.85   $144.80  
  Purchase #7 $82.70   12.514%   $93.0491   $93.05   $93.05   $93.00  
  7 purchase totals = $1,052.70       $1,173.8953   $1,173.90   $1,173.90   $1,173.80