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 $87.28   4.505%   $91.212   $91.21   $91.20   $91.20  
  Purchase #2 $64.60   8.163%   $69.8733   $69.87   $69.85   $69.90  
  Purchase #3 $114.32   6.394%   $121.6296   $121.63   $121.65   $121.60  
  Purchase #4 $243.94   7.661%   $262.6282   $262.63   $262.65   $262.60  
  Purchase #5 $98.66   10.689%   $109.2058   $109.21   $109.20   $109.20  
  Purchase #6 $150.81   3.182%   $155.6088   $155.61   $155.60   $155.60  
  Purchase #7 $210.96   5.165%   $221.8561   $221.86   $221.85   $221.90  
  7 purchase totals = $970.57       $1,032.0138   $1,032.02   $1,032.00   $1,032.00