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 $66.25   7.181%   $71.0074   $71.01   $71.00   $71.00  
  Purchase #2 $224.61   8.427%   $243.5379   $243.54   $243.55   $243.50  
  Purchase #3 $170.96   9.345%   $186.9362   $186.94   $186.95   $186.90  
  Purchase #4 $76.66   6.523%   $81.6605   $81.66   $81.65   $81.70  
  Purchase #5 $185.67   3.862%   $192.8406   $192.84   $192.85   $192.80  
  Purchase #6 $235.37   4.871%   $246.8349   $246.83   $246.85   $246.80  
  Purchase #7 $215.85   11.759%   $241.2318   $241.23   $241.25   $241.20  
  7 purchase totals = $1,175.37       $1,264.0493   $1,264.05   $1,264.10   $1,263.90