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 $216.72   13.516%   $246.0119   $246.01   $246.00   $246.00  
  Purchase #2 $38.76   7.810%   $41.7872   $41.79   $41.80   $41.80  
  Purchase #3 $235.36   10.590%   $260.2846   $260.28   $260.30   $260.30  
  Purchase #4 $184.37   11.636%   $205.8233   $205.82   $205.80   $205.80  
  Purchase #5 $230.36   4.222%   $240.0858   $240.09   $240.10   $240.10  
  Purchase #6 $7.90   9.417%   $8.6439   $8.64   $8.65   $8.60  
  Purchase #7 $250.47   5.798%   $264.9923   $264.99   $265.00   $265.00  
  7 purchase totals = $1,163.94       $1,267.6290   $1,267.62   $1,267.65   $1,267.60