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 $246.58   11.197%   $274.1896   $274.19   $274.20   $274.20  
  Purchase #2 $159.46   9.827%   $175.1301   $175.13   $175.15   $175.10  
  Purchase #3 $160.27   7.499%   $172.2886   $172.29   $172.30   $172.30  
  Purchase #4 $52.68   13.801%   $59.9504   $59.95   $59.95   $60.00  
  Purchase #5 $164.91   10.698%   $182.5521   $182.55   $182.55   $182.60  
  Purchase #6 $111.78   5.710%   $118.1626   $118.16   $118.15   $118.20  
  Purchase #7 $76.28   5.351%   $80.3617   $80.36   $80.35   $80.40  
  7 purchase totals = $971.96       $1,062.6351   $1,062.63   $1,062.65   $1,062.80