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 $170.26   6.536%   $181.3882   $181.39   $181.40   $181.40  
  Purchase #2 $207.78   3.553%   $215.1624   $215.16   $215.15   $215.20  
  Purchase #3 $168.79   6.656%   $180.0247   $180.02   $180.00   $180.00  
  Purchase #4 $11.50   11.698%   $12.8453   $12.85   $12.85   $12.80  
  Purchase #5 $222.77   3.472%   $230.5046   $230.50   $230.50   $230.50  
  Purchase #6 $22.29   9.521%   $24.4122   $24.41   $24.40   $24.40  
  Purchase #7 $178.97   9.333%   $195.6733   $195.67   $195.65   $195.70  
  7 purchase totals = $982.36       $1,040.0107   $1,040.00   $1,039.95   $1,040.00