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 $58.93   6.213%   $62.5913   $62.59   $62.60   $62.60  
  Purchase #2 $206.30   13.782%   $234.7323   $234.73   $234.75   $234.70  
  Purchase #3 $75.33   12.505%   $84.75   $84.75   $84.75   $84.80  
  Purchase #4 $18.77   12.477%   $21.1119   $21.11   $21.10   $21.10  
  Purchase #5 $24.99   5.789%   $26.4367   $26.44   $26.45   $26.40  
  Purchase #6 $6.94   5.315%   $7.3089   $7.31   $7.30   $7.30  
  Purchase #7 $155.68   5.353%   $164.0136   $164.01   $164.00   $164.00  
  7 purchase totals = $546.94       $600.9447   $600.94   $600.95   $600.90