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 $223.91   6.495%   $238.453   $238.45   $238.45   $238.50  
  Purchase #2 $237.68   12.705%   $267.8772   $267.88   $267.90   $267.90  
  Purchase #3 $196.78   7.144%   $210.838   $210.84   $210.85   $210.80  
  Purchase #4 $122.87   13.737%   $139.7487   $139.75   $139.75   $139.70  
  Purchase #5 $188.25   3.422%   $194.6919   $194.69   $194.70   $194.70  
  Purchase #6 $240.26   9.337%   $262.6931   $262.69   $262.70   $262.70  
  Purchase #7 $41.37   7.561%   $44.498   $44.50   $44.50   $44.50  
  7 purchase totals = $1,251.12       $1,358.7999   $1,358.80   $1,358.85   $1,358.80