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 $66.81   13.213%   $75.6376   $75.64   $75.65   $75.60  
  Purchase #2 $114.31   5.582%   $120.6908   $120.69   $120.70   $120.70  
  Purchase #3 $214.48   10.434%   $236.8588   $236.86   $236.85   $236.90  
  Purchase #4 $209.69   3.240%   $216.484   $216.48   $216.50   $216.50  
  Purchase #5 $214.42   10.160%   $236.2051   $236.21   $236.20   $236.20  
  Purchase #6 $21.53   6.612%   $22.9536   $22.95   $22.95   $23.00  
  Purchase #7 $145.84   10.691%   $161.4318   $161.43   $161.45   $161.40  
  7 purchase totals = $987.08       $1,070.2617   $1,070.26   $1,070.30   $1,070.30