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 $72.95   12.277%   $81.9061   $81.91   $81.90   $81.90  
  Purchase #2 $205.58   4.693%   $215.2279   $215.23   $215.25   $215.20  
  Purchase #3 $83.84   10.568%   $92.7002   $92.70   $92.70   $92.70  
  Purchase #4 $144.49   10.577%   $159.7727   $159.77   $159.75   $159.80  
  Purchase #5 $58.65   7.833%   $63.2441   $63.24   $63.25   $63.20  
  Purchase #6 $216.86   8.536%   $235.3712   $235.37   $235.35   $235.40  
  Purchase #7 $202.39   9.708%   $222.038   $222.04   $222.05   $222.00  
  7 purchase totals = $984.76       $1,070.2602   $1,070.26   $1,070.25   $1,070.20