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 $108.46   4.561%   $113.4069   $113.41   $113.40   $113.40  
  Purchase #2 $221.94   6.627%   $236.648   $236.65   $236.65   $236.60  
  Purchase #3 $14.98   3.522%   $15.5076   $15.51   $15.50   $15.50  
  Purchase #4 $60.70   13.872%   $69.1203   $69.12   $69.10   $69.10  
  Purchase #5 $223.49   9.841%   $245.4837   $245.48   $245.50   $245.50  
  Purchase #6 $197.90   4.268%   $206.3464   $206.35   $206.35   $206.30  
  Purchase #7 $139.56   6.642%   $148.8296   $148.83   $148.85   $148.80  
  7 purchase totals = $967.03       $1,035.3425   $1,035.35   $1,035.35   $1,035.20