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 $241.97   3.319%   $250.001   $250.00   $250.00   $250.00  
  Purchase #2 $186.42   10.491%   $205.9773   $205.98   $206.00   $206.00  
  Purchase #3 $150.83   6.280%   $160.3021   $160.30   $160.30   $160.30  
  Purchase #4 $105.41   6.395%   $112.151   $112.15   $112.15   $112.20  
  Purchase #5 $168.51   5.501%   $177.7797   $177.78   $177.80   $177.80  
  Purchase #6 $82.42   12.680%   $92.8709   $92.87   $92.85   $92.90  
  Purchase #7 $120.47   13.169%   $136.3347   $136.33   $136.35   $136.30  
  7 purchase totals = $1,056.03       $1,135.4167   $1,135.41   $1,135.45   $1,135.50