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 $88.66   10.579%   $98.0393   $98.04   $98.05   $98.00  
  Purchase #2 $44.69   3.204%   $46.1219   $46.12   $46.10   $46.10  
  Purchase #3 $48.71   8.219%   $52.7135   $52.71   $52.70   $52.70  
  Purchase #4 $193.80   10.313%   $213.7866   $213.79   $213.80   $213.80  
  Purchase #5 $97.59   13.690%   $110.9501   $110.95   $110.95   $111.00  
  Purchase #6 $63.74   8.738%   $69.3096   $69.31   $69.30   $69.30  
  Purchase #7 $175.75   7.620%   $189.1422   $189.14   $189.15   $189.10  
  7 purchase totals = $712.94       $780.0632   $780.06   $780.05   $780.00