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 $46.81   12.234%   $52.5367   $52.54   $52.55   $52.50  
  Purchase #2 $213.53   8.477%   $231.6309   $231.63   $231.65   $231.60  
  Purchase #3 $17.90   5.736%   $18.9267   $18.93   $18.95   $18.90  
  Purchase #4 $71.38   13.523%   $81.0327   $81.03   $81.05   $81.00  
  Purchase #5 $163.99   7.261%   $175.8973   $175.90   $175.90   $175.90  
  Purchase #6 $162.44   11.224%   $180.6723   $180.67   $180.65   $180.70  
  Purchase #7 $59.43   5.450%   $62.6689   $62.67   $62.65   $62.70  
  7 purchase totals = $735.48       $803.3655   $803.37   $803.40   $803.30