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 $224.83   8.498%   $243.9361   $243.94   $243.95   $243.90  
  Purchase #2 $89.26   3.485%   $92.3707   $92.37   $92.35   $92.40  
  Purchase #3 $181.46   10.425%   $200.3772   $200.38   $200.40   $200.40  
  Purchase #4 $23.74   13.777%   $27.0107   $27.01   $27.00   $27.00  
  Purchase #5 $18.71   7.623%   $20.1363   $20.14   $20.15   $20.10  
  Purchase #6 $194.28   5.549%   $205.0606   $205.06   $205.05   $205.10  
  Purchase #7 $214.72   8.246%   $232.4258   $232.43   $232.45   $232.40  
  7 purchase totals = $947.00       $1,021.3174   $1,021.33   $1,021.35   $1,021.30