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 $247.93   7.548%   $266.6438   $266.64   $266.65   $266.60  
  Purchase #2 $229.64   5.203%   $241.5882   $241.59   $241.60   $241.60  
  Purchase #3 $224.77   4.695%   $235.323   $235.32   $235.30   $235.30  
  Purchase #4 $126.26   10.300%   $139.2648   $139.26   $139.25   $139.30  
  Purchase #5 $8.27   3.836%   $8.5872   $8.59   $8.60   $8.60  
  Purchase #6 $138.36   11.849%   $154.7543   $154.75   $154.75   $154.80  
  Purchase #7 $24.42   3.842%   $25.3582   $25.36   $25.35   $25.40  
  7 purchase totals = $999.65       $1,071.5195   $1,071.51   $1,071.50   $1,071.60