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 $244.67   12.771%   $275.9168   $275.92   $275.90   $275.90  
  Purchase #2 $67.63   13.495%   $76.7567   $76.76   $76.75   $76.80  
  Purchase #3 $242.42   11.740%   $270.8801   $270.88   $270.90   $270.90  
  Purchase #4 $78.66   5.807%   $83.2278   $83.23   $83.25   $83.20  
  Purchase #5 $92.32   6.173%   $98.0189   $98.02   $98.00   $98.00  
  Purchase #6 $221.39   5.400%   $233.3451   $233.35   $233.35   $233.30  
  Purchase #7 $236.73   12.307%   $265.8644   $265.86   $265.85   $265.90  
  7 purchase totals = $1,183.82       $1,304.0098   $1,304.02   $1,304.00   $1,304.00