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 $86.60   12.867%   $97.7428   $97.74   $97.75   $97.70  
  Purchase #2 $91.28   4.765%   $95.6295   $95.63   $95.65   $95.60  
  Purchase #3 $244.53   3.394%   $252.8293   $252.83   $252.85   $252.80  
  Purchase #4 $30.87   9.274%   $33.7329   $33.73   $33.75   $33.70  
  Purchase #5 $73.64   10.258%   $81.194   $81.19   $81.20   $81.20  
  Purchase #6 $195.71   4.352%   $204.2273   $204.23   $204.25   $204.20  
  Purchase #7 $58.61   4.127%   $61.0288   $61.03   $61.05   $61.00  
  7 purchase totals = $781.24       $826.3846   $826.38   $826.50   $826.20