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 $244.77   8.135%   $264.682   $264.68   $264.70   $264.70  
  Purchase #2 $57.73   6.570%   $61.5229   $61.52   $61.50   $61.50  
  Purchase #3 $72.83   9.396%   $79.6731   $79.67   $79.65   $79.70  
  Purchase #4 $223.81   5.404%   $235.9047   $235.90   $235.90   $235.90  
  Purchase #5 $73.55   3.859%   $76.3883   $76.39   $76.40   $76.40  
  Purchase #6 $142.28   8.663%   $154.6057   $154.61   $154.60   $154.60  
  Purchase #7 $69.49   8.697%   $75.5335   $75.53   $75.55   $75.50  
  7 purchase totals = $884.46       $948.3102   $948.30   $948.30   $948.30