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 $206.50   8.386%   $223.8171   $223.82   $223.80   $223.80  
  Purchase #2 $23.76   10.419%   $26.2356   $26.24   $26.25   $26.20  
  Purchase #3 $165.78   13.818%   $188.6875   $188.69   $188.70   $188.70  
  Purchase #4 $158.80   8.709%   $172.6299   $172.63   $172.65   $172.60  
  Purchase #5 $168.80   5.378%   $177.8781   $177.88   $177.90   $177.90  
  Purchase #6 $111.53   3.201%   $115.1001   $115.10   $115.10   $115.10  
  Purchase #7 $202.46   6.860%   $216.3488   $216.35   $216.35   $216.30  
  7 purchase totals = $1,037.63       $1,120.6971   $1,120.71   $1,120.75   $1,120.60