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 $227.44   8.216%   $246.1265   $246.13   $246.15   $246.10  
  Purchase #2 $181.65   9.552%   $199.0012   $199.00   $199.00   $199.00  
  Purchase #3 $191.51   11.813%   $214.1331   $214.13   $214.15   $214.10  
  Purchase #4 $98.41   6.369%   $104.6777   $104.68   $104.70   $104.70  
  Purchase #5 $239.36   11.506%   $266.9008   $266.90   $266.90   $266.90  
  Purchase #6 $39.56   12.116%   $44.3531   $44.35   $44.35   $44.40  
  Purchase #7 $168.27   13.756%   $191.4172   $191.42   $191.40   $191.40  
  7 purchase totals = $1,146.20       $1,266.6096   $1,266.61   $1,266.65   $1,266.60