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 $67.97   8.420%   $73.6931   $73.69   $73.70   $73.70  
  Purchase #2 $147.58   11.596%   $164.6934   $164.69   $164.70   $164.70  
  Purchase #3 $67.60   8.123%   $73.0911   $73.09   $73.10   $73.10  
  Purchase #4 $214.45   13.576%   $243.5637   $243.56   $243.55   $243.60  
  Purchase #5 $15.61   5.404%   $16.4536   $16.45   $16.45   $16.50  
  Purchase #6 $178.78   5.873%   $189.2797   $189.28   $189.30   $189.30  
  Purchase #7 $71.81   6.237%   $76.2888   $76.29   $76.30   $76.30  
  7 purchase totals = $763.80       $837.0634   $837.05   $837.10   $837.20