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 $170.95   11.726%   $190.9956   $191.00   $191.00   $191.00  
  Purchase #2 $203.90   5.778%   $215.6813   $215.68   $215.70   $215.70  
  Purchase #3 $23.77   4.415%   $24.8194   $24.82   $24.80   $24.80  
  Purchase #4 $61.34   10.512%   $67.7881   $67.79   $67.80   $67.80  
  Purchase #5 $54.92   9.792%   $60.2978   $60.30   $60.30   $60.30  
  Purchase #6 $186.60   11.253%   $207.5981   $207.60   $207.60   $207.60  
  Purchase #7 $22.63   13.658%   $25.7208   $25.72   $25.70   $25.70  
  7 purchase totals = $724.11       $792.9011   $792.91   $792.90   $792.90