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 $53.77   7.784%   $57.9555   $57.96   $57.95   $58.00  
  Purchase #2 $176.35   5.750%   $186.4901   $186.49   $186.50   $186.50  
  Purchase #3 $66.33   10.747%   $73.4585   $73.46   $73.45   $73.50  
  Purchase #4 $121.62   7.645%   $130.9178   $130.92   $130.90   $130.90  
  Purchase #5 $250.94   10.428%   $277.108   $277.11   $277.10   $277.10  
  Purchase #6 $59.54   10.330%   $65.6905   $65.69   $65.70   $65.70  
  Purchase #7 $83.51   8.720%   $90.7921   $90.79   $90.80   $90.80  
  7 purchase totals = $812.06       $882.4125   $882.42   $882.40   $882.50