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 $84.61   12.845%   $95.4782   $95.48   $95.50   $95.50  
  Purchase #2 $48.40   12.661%   $54.5279   $54.53   $54.55   $54.50  
  Purchase #3 $176.76   8.512%   $191.8058   $191.81   $191.80   $191.80  
  Purchase #4 $220.48   10.218%   $243.0086   $243.01   $243.00   $243.00  
  Purchase #5 $6.84   4.217%   $7.1284   $7.13   $7.15   $7.10  
  Purchase #6 $197.94   4.766%   $207.3738   $207.37   $207.35   $207.40  
  Purchase #7 $23.71   12.579%   $26.6925   $26.69   $26.70   $26.70  
  7 purchase totals = $758.74       $826.0152   $826.02   $826.05   $826.00