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 $221.26   9.828%   $243.0054   $243.01   $243.00   $243.00  
  Purchase #2 $136.73   9.414%   $149.6018   $149.60   $149.60   $149.60  
  Purchase #3 $17.76   11.848%   $19.8642   $19.86   $19.85   $19.90  
  Purchase #4 $166.48   8.627%   $180.8422   $180.84   $180.85   $180.80  
  Purchase #5 $207.81   4.554%   $217.2737   $217.27   $217.25   $217.30  
  Purchase #6 $130.35   11.450%   $145.2751   $145.28   $145.30   $145.30  
  Purchase #7 $226.82   10.564%   $250.7813   $250.78   $250.80   $250.80  
  7 purchase totals = $1,107.21       $1,206.6437   $1,206.64   $1,206.65   $1,206.70