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 $219.53   5.808%   $232.2803   $232.28   $232.30   $232.30  
  Purchase #2 $9.50   11.497%   $10.5922   $10.59   $10.60   $10.60  
  Purchase #3 $228.88   9.581%   $250.809   $250.81   $250.80   $250.80  
  Purchase #4 $149.50   11.670%   $166.9467   $166.95   $166.95   $166.90  
  Purchase #5 $244.34   6.151%   $259.3694   $259.37   $259.35   $259.40  
  Purchase #6 $167.82   3.114%   $173.0459   $173.05   $173.05   $173.00  
  Purchase #7 $185.56   11.376%   $206.6693   $206.67   $206.65   $206.70  
  7 purchase totals = $1,205.13       $1,299.7128   $1,299.72   $1,299.70   $1,299.70