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 $67.62   10.541%   $74.7478   $74.75   $74.75   $74.70  
  Purchase #2 $115.91   9.335%   $126.7302   $126.73   $126.75   $126.70  
  Purchase #3 $134.81   5.316%   $141.9765   $141.98   $142.00   $142.00  
  Purchase #4 $186.46   5.643%   $196.9819   $196.98   $197.00   $197.00  
  Purchase #5 $132.53   13.317%   $150.179   $150.18   $150.20   $150.20  
  Purchase #6 $231.53   11.488%   $258.1282   $258.13   $258.15   $258.10  
  Purchase #7 $209.29   4.670%   $219.0638   $219.06   $219.05   $219.10  
  7 purchase totals = $1,078.15       $1,167.8074   $1,167.81   $1,167.90   $1,167.80