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 $218.65   11.443%   $243.6701   $243.67   $243.65   $243.70  
  Purchase #2 $164.94   6.774%   $176.113   $176.11   $176.10   $176.10  
  Purchase #3 $109.79   8.734%   $119.3791   $119.38   $119.40   $119.40  
  Purchase #4 $249.98   13.745%   $284.3398   $284.34   $284.35   $284.30  
  Purchase #5 $199.90   3.800%   $207.4962   $207.50   $207.50   $207.50  
  Purchase #6 $60.99   5.414%   $64.292   $64.29   $64.30   $64.30  
  Purchase #7 $56.68   12.842%   $63.9588   $63.96   $63.95   $64.00  
  7 purchase totals = $1,060.93       $1,159.2490   $1,159.25   $1,159.25   $1,159.30