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 $184.68   10.855%   $204.727   $204.73   $204.75   $204.70  
  Purchase #2 $44.96   11.804%   $50.2671   $50.27   $50.25   $50.30  
  Purchase #3 $135.35   7.530%   $145.5419   $145.54   $145.55   $145.50  
  Purchase #4 $94.93   6.605%   $101.2001   $101.20   $101.20   $101.20  
  Purchase #5 $121.77   11.679%   $135.9915   $135.99   $136.00   $136.00  
  Purchase #6 $171.65   5.159%   $180.5054   $180.51   $180.50   $180.50  
  Purchase #7 $56.42   3.691%   $58.5025   $58.50   $58.50   $58.50  
  7 purchase totals = $809.76       $876.7355   $876.74   $876.75   $876.70