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 $101.47   6.448%   $108.0128   $108.01   $108.00   $108.00  
  Purchase #2 $37.31   10.857%   $41.3607   $41.36   $41.35   $41.40  
  Purchase #3 $227.88   9.658%   $249.8887   $249.89   $249.90   $249.90  
  Purchase #4 $132.73   4.637%   $138.8847   $138.88   $138.90   $138.90  
  Purchase #5 $185.73   9.594%   $203.5489   $203.55   $203.55   $203.50  
  Purchase #6 $236.75   8.655%   $257.2407   $257.24   $257.25   $257.20  
  Purchase #7 $32.61   11.419%   $36.3337   $36.33   $36.35   $36.30  
  7 purchase totals = $954.48       $1,035.2702   $1,035.26   $1,035.30   $1,035.20