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 $136.57   10.667%   $151.1379   $151.14   $151.15   $151.10  
  Purchase #2 $216.59   13.868%   $246.6267   $246.63   $246.65   $246.60  
  Purchase #3 $115.58   9.116%   $126.1163   $126.12   $126.10   $126.10  
  Purchase #4 $79.97   7.493%   $85.9622   $85.96   $85.95   $86.00  
  Purchase #5 $215.56   13.467%   $244.5895   $244.59   $244.60   $244.60  
  Purchase #6 $235.49   11.838%   $263.3673   $263.37   $263.35   $263.40  
  Purchase #7 $40.64   10.639%   $44.9637   $44.96   $44.95   $45.00  
  7 purchase totals = $1,040.40       $1,162.7636   $1,162.77   $1,162.75   $1,162.80