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 $242.53   10.381%   $267.707   $267.71   $267.70   $267.70  
  Purchase #2 $62.62   12.207%   $70.264   $70.26   $70.25   $70.30  
  Purchase #3 $116.77   8.148%   $126.2844   $126.28   $126.30   $126.30  
  Purchase #4 $240.63   6.618%   $256.5549   $256.55   $256.55   $256.60  
  Purchase #5 $210.87   13.215%   $238.7365   $238.74   $238.75   $238.70  
  Purchase #6 $123.47   9.826%   $135.6022   $135.60   $135.60   $135.60  
  Purchase #7 $111.75   9.343%   $122.1908   $122.19   $122.20   $122.20  
  7 purchase totals = $1,108.64       $1,217.3398   $1,217.33   $1,217.35   $1,217.40