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 $152.63   3.326%   $157.7065   $157.71   $157.70   $157.70  
  Purchase #2 $219.78   7.202%   $235.6086   $235.61   $235.60   $235.60  
  Purchase #3 $112.32   7.570%   $120.8226   $120.82   $120.80   $120.80  
  Purchase #4 $58.27   12.464%   $65.5328   $65.53   $65.55   $65.50  
  Purchase #5 $239.78   11.408%   $267.1341   $267.13   $267.15   $267.10  
  Purchase #6 $128.68   3.129%   $132.7064   $132.71   $132.70   $132.70  
  Purchase #7 $234.90   4.767%   $246.0977   $246.10   $246.10   $246.10  
  7 purchase totals = $1,146.36       $1,225.6087   $1,225.61   $1,225.60   $1,225.50