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 $244.91   12.484%   $275.4846   $275.48   $275.50   $275.50  
  Purchase #2 $20.26   9.474%   $22.1794   $22.18   $22.20   $22.20  
  Purchase #3 $44.32   5.537%   $46.774   $46.77   $46.75   $46.80  
  Purchase #4 $157.74   10.137%   $173.7301   $173.73   $173.75   $173.70  
  Purchase #5 $233.96   5.456%   $246.7249   $246.72   $246.70   $246.70  
  Purchase #6 $96.78   10.183%   $106.6351   $106.64   $106.65   $106.60  
  Purchase #7 $159.74   13.234%   $180.88   $180.88   $180.90   $180.90  
  7 purchase totals = $957.71       $1,052.4081   $1,052.40   $1,052.45   $1,052.40