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 $236.38   10.216%   $260.5286   $260.53   $260.55   $260.50  
  Purchase #2 $133.43   7.314%   $143.1891   $143.19   $143.20   $143.20  
  Purchase #3 $118.35   5.722%   $125.122   $125.12   $125.10   $125.10  
  Purchase #4 $195.84   6.191%   $207.9645   $207.96   $207.95   $208.00  
  Purchase #5 $179.74   7.196%   $192.6741   $192.67   $192.65   $192.70  
  Purchase #6 $64.94   11.599%   $72.4724   $72.47   $72.45   $72.50  
  Purchase #7 $92.77   10.722%   $102.7168   $102.72   $102.70   $102.70  
  7 purchase totals = $1,021.45       $1,104.6675   $1,104.66   $1,104.60   $1,104.70