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 $216.48   3.427%   $223.8988   $223.90   $223.90   $223.90  
  Purchase #2 $96.84   4.810%   $101.498   $101.50   $101.50   $101.50  
  Purchase #3 $8.72   10.549%   $9.6399   $9.64   $9.65   $9.60  
  Purchase #4 $236.65   12.811%   $266.9672   $266.97   $266.95   $267.00  
  Purchase #5 $187.73   7.712%   $202.2077   $202.21   $202.20   $202.20  
  Purchase #6 $211.85   13.756%   $240.9921   $240.99   $241.00   $241.00  
  Purchase #7 $229.69   12.233%   $257.788   $257.79   $257.80   $257.80  
  7 purchase totals = $1,187.96       $1,302.9917   $1,303.00   $1,303.00   $1,303.00