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 $114.71   10.203%   $126.4139   $126.41   $126.40   $126.40  
  Purchase #2 $193.64   10.355%   $213.6914   $213.69   $213.70   $213.70  
  Purchase #3 $212.89   13.165%   $240.917   $240.92   $240.90   $240.90  
  Purchase #4 $90.79   9.551%   $99.4614   $99.46   $99.45   $99.50  
  Purchase #5 $243.91   13.756%   $277.4623   $277.46   $277.45   $277.50  
  Purchase #6 $59.36   7.381%   $63.7414   $63.74   $63.75   $63.70  
  Purchase #7 $123.25   10.559%   $136.264   $136.26   $136.25   $136.30  
  7 purchase totals = $1,038.55       $1,157.9514   $1,157.94   $1,157.90   $1,158.00