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 $223.40   10.693%   $247.2882   $247.29   $247.30   $247.30  
  Purchase #2 $24.93   4.447%   $26.0386   $26.04   $26.05   $26.00  
  Purchase #3 $158.53   9.364%   $173.3747   $173.37   $173.35   $173.40  
  Purchase #4 $206.27   12.121%   $231.272   $231.27   $231.25   $231.30  
  Purchase #5 $115.56   5.255%   $121.6327   $121.63   $121.65   $121.60  
  Purchase #6 $173.27   4.745%   $181.4917   $181.49   $181.50   $181.50  
  Purchase #7 $78.40   5.339%   $82.5858   $82.59   $82.60   $82.60  
  7 purchase totals = $980.36       $1,063.6837   $1,063.68   $1,063.70   $1,063.70