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 $217.45   11.619%   $242.7155   $242.72   $242.70   $242.70  
  Purchase #2 $16.26   6.673%   $17.345   $17.35   $17.35   $17.30  
  Purchase #3 $15.73   13.865%   $17.911   $17.91   $17.90   $17.90  
  Purchase #4 $50.30   4.676%   $52.652   $52.65   $52.65   $52.70  
  Purchase #5 $217.93   3.732%   $226.0631   $226.06   $226.05   $226.10  
  Purchase #6 $232.60   9.512%   $254.7249   $254.72   $254.70   $254.70  
  Purchase #7 $239.39   4.348%   $249.7987   $249.80   $249.80   $249.80  
  7 purchase totals = $989.66       $1,061.2102   $1,061.21   $1,061.15   $1,061.20