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 $228.38   10.707%   $252.8326   $252.83   $252.85   $252.80  
  Purchase #2 $102.65   13.652%   $116.6638   $116.66   $116.65   $116.70  
  Purchase #3 $146.52   4.138%   $152.583   $152.58   $152.60   $152.60  
  Purchase #4 $11.53   8.501%   $12.5102   $12.51   $12.50   $12.50  
  Purchase #5 $228.48   9.721%   $250.6905   $250.69   $250.70   $250.70  
  Purchase #6 $31.77   12.474%   $35.733   $35.73   $35.75   $35.70  
  Purchase #7 $241.87   7.748%   $260.6101   $260.61   $260.60   $260.60  
  7 purchase totals = $991.20       $1,081.6232   $1,081.61   $1,081.65   $1,081.60