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 $224.41   8.473%   $243.4243   $243.42   $243.40   $243.40  
  Purchase #2 $232.44   7.414%   $249.6731   $249.67   $249.65   $249.70  
  Purchase #3 $106.71   4.874%   $111.911   $111.91   $111.90   $111.90  
  Purchase #4 $151.81   6.803%   $162.1376   $162.14   $162.15   $162.10  
  Purchase #5 $238.97   5.280%   $251.5876   $251.59   $251.60   $251.60  
  Purchase #6 $137.44   11.417%   $153.1315   $153.13   $153.15   $153.10  
  Purchase #7 $7.65   4.621%   $8.0035   $8.00   $8.00   $8.00  
  7 purchase totals = $1,099.43       $1,179.8686   $1,179.86   $1,179.85   $1,179.80