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 $207.76   8.822%   $226.0886   $226.09   $226.10   $226.10  
  Purchase #2 $93.54   5.249%   $98.4499   $98.45   $98.45   $98.40  
  Purchase #3 $202.29   7.617%   $217.6984   $217.70   $217.70   $217.70  
  Purchase #4 $240.28   4.306%   $250.6265   $250.63   $250.65   $250.60  
  Purchase #5 $202.82   4.655%   $212.2613   $212.26   $212.25   $212.30  
  Purchase #6 $88.63   3.272%   $91.53   $91.53   $91.55   $91.50  
  Purchase #7 $194.94   6.653%   $207.9094   $207.91   $207.90   $207.90  
  7 purchase totals = $1,230.26       $1,304.5641   $1,304.57   $1,304.60   $1,304.50