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 $222.51   10.719%   $246.3608   $246.36   $246.35   $246.40  
  Purchase #2 $185.49   7.663%   $199.7041   $199.70   $199.70   $199.70  
  Purchase #3 $222.76   9.686%   $244.3365   $244.34   $244.35   $244.30  
  Purchase #4 $89.81   6.237%   $95.4114   $95.41   $95.40   $95.40  
  Purchase #5 $18.26   11.773%   $20.4097   $20.41   $20.40   $20.40  
  Purchase #6 $129.34   11.782%   $144.5788   $144.58   $144.60   $144.60  
  Purchase #7 $48.47   5.253%   $51.0161   $51.02   $51.00   $51.00  
  7 purchase totals = $916.64       $1,001.8174   $1,001.82   $1,001.80   $1,001.80