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 $58.25   13.383%   $66.0456   $66.05   $66.05   $66.00  
  Purchase #2 $214.89   5.314%   $226.3093   $226.31   $226.30   $226.30  
  Purchase #3 $15.30   5.666%   $16.1669   $16.17   $16.15   $16.20  
  Purchase #4 $29.76   11.814%   $33.2758   $33.28   $33.30   $33.30  
  Purchase #5 $95.53   5.268%   $100.5625   $100.56   $100.55   $100.60  
  Purchase #6 $195.45   13.560%   $221.953   $221.95   $221.95   $222.00  
  Purchase #7 $150.65   7.538%   $162.006   $162.01   $162.00   $162.00  
  7 purchase totals = $759.83       $826.3191   $826.33   $826.30   $826.40