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 $182.40   11.218%   $202.8616   $202.86   $202.85   $202.90  
  Purchase #2 $165.66   9.429%   $181.2801   $181.28   $181.30   $181.30  
  Purchase #3 $24.94   7.331%   $26.7684   $26.77   $26.75   $26.80  
  Purchase #4 $156.87   13.525%   $178.0867   $178.09   $178.10   $178.10  
  Purchase #5 $54.84   5.750%   $57.9933   $57.99   $58.00   $58.00  
  Purchase #6 $30.51   13.550%   $34.6441   $34.64   $34.65   $34.60  
  Purchase #7 $242.39   10.176%   $267.0556   $267.06   $267.05   $267.10  
  7 purchase totals = $857.61       $948.6898   $948.69   $948.70   $948.80