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 $65.94   11.521%   $73.5369   $73.54   $73.55   $73.50  
  Purchase #2 $202.80   3.406%   $209.7074   $209.71   $209.70   $209.70  
  Purchase #3 $210.88   9.573%   $231.0675   $231.07   $231.05   $231.10  
  Purchase #4 $123.97   6.468%   $131.9884   $131.99   $132.00   $132.00  
  Purchase #5 $200.68   4.847%   $210.407   $210.41   $210.40   $210.40  
  Purchase #6 $187.67   10.438%   $207.259   $207.26   $207.25   $207.30  
  Purchase #7 $172.43   11.501%   $192.2612   $192.26   $192.25   $192.30  
  7 purchase totals = $1,164.37       $1,256.2274   $1,256.24   $1,256.20   $1,256.30