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 $149.87   11.404%   $166.9612   $166.96   $166.95   $167.00  
  Purchase #2 $156.34   4.355%   $163.1486   $163.15   $163.15   $163.10  
  Purchase #3 $143.43   11.739%   $160.2672   $160.27   $160.25   $160.30  
  Purchase #4 $56.58   6.560%   $60.2916   $60.29   $60.30   $60.30  
  Purchase #5 $55.84   3.403%   $57.7402   $57.74   $57.75   $57.70  
  Purchase #6 $9.63   6.312%   $10.2378   $10.24   $10.25   $10.20  
  Purchase #7 $213.79   6.450%   $227.5795   $227.58   $227.60   $227.60  
  7 purchase totals = $785.48       $846.2261   $846.23   $846.25   $846.20