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 $244.62   9.816%   $268.6319   $268.63   $268.65   $268.60  
  Purchase #2 $65.82   7.864%   $70.9961   $71.00   $71.00   $71.00  
  Purchase #3 $27.65   5.534%   $29.1802   $29.18   $29.20   $29.20  
  Purchase #4 $233.79   13.243%   $264.7508   $264.75   $264.75   $264.80  
  Purchase #5 $208.62   4.366%   $217.7283   $217.73   $217.75   $217.70  
  Purchase #6 $236.61   11.318%   $263.3895   $263.39   $263.40   $263.40  
  Purchase #7 $208.51   5.286%   $219.5318   $219.53   $219.55   $219.50  
  7 purchase totals = $1,225.62       $1,334.2086   $1,334.21   $1,334.30   $1,334.20