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 $165.80   13.540%   $188.2493   $188.25   $188.25   $188.20  
  Purchase #2 $234.67   13.498%   $266.3458   $266.35   $266.35   $266.30  
  Purchase #3 $85.48   12.261%   $95.9607   $95.96   $95.95   $96.00  
  Purchase #4 $10.82   12.569%   $12.18   $12.18   $12.20   $12.20  
  Purchase #5 $50.28   5.453%   $53.0218   $53.02   $53.00   $53.00  
  Purchase #6 $31.87   4.330%   $33.25   $33.25   $33.25   $33.30  
  Purchase #7 $233.79   13.678%   $265.7678   $265.77   $265.75   $265.80  
  7 purchase totals = $812.71       $914.7754   $914.78   $914.75   $914.80