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 $138.31   11.448%   $154.1437   $154.14   $154.15   $154.10  
  Purchase #2 $213.86   9.813%   $234.8461   $234.85   $234.85   $234.80  
  Purchase #3 $27.55   8.739%   $29.9576   $29.96   $29.95   $30.00  
  Purchase #4 $96.97   8.420%   $105.1349   $105.13   $105.15   $105.10  
  Purchase #5 $29.80   10.250%   $32.8545   $32.85   $32.85   $32.90  
  Purchase #6 $26.63   12.553%   $29.9729   $29.97   $29.95   $30.00  
  Purchase #7 $160.66   5.267%   $169.122   $169.12   $169.10   $169.10  
  7 purchase totals = $693.78       $756.0317   $756.02   $756.00   $756.00