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 $188.79   3.811%   $195.9848   $195.98   $196.00   $196.00  
  Purchase #2 $136.39   7.781%   $147.0025   $147.00   $147.00   $147.00  
  Purchase #3 $82.28   6.212%   $87.3912   $87.39   $87.40   $87.40  
  Purchase #4 $75.63   10.871%   $83.8517   $83.85   $83.85   $83.90  
  Purchase #5 $192.78   9.696%   $211.4719   $211.47   $211.45   $211.50  
  Purchase #6 $35.94   10.862%   $39.8438   $39.84   $39.85   $39.80  
  Purchase #7 $209.78   12.742%   $236.5102   $236.51   $236.50   $236.50  
  7 purchase totals = $921.59       $1,002.0561   $1,002.04   $1,002.05   $1,002.10