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 $111.89   11.147%   $124.3624   $124.36   $124.35   $124.40  
  Purchase #2 $103.52   5.172%   $108.8741   $108.87   $108.85   $108.90  
  Purchase #3 $43.62   11.613%   $48.6856   $48.69   $48.70   $48.70  
  Purchase #4 $118.90   13.415%   $134.8504   $134.85   $134.85   $134.90  
  Purchase #5 $153.67   3.691%   $159.342   $159.34   $159.35   $159.30  
  Purchase #6 $211.72   11.129%   $235.2823   $235.28   $235.30   $235.30  
  Purchase #7 $224.62   5.404%   $236.7585   $236.76   $236.75   $236.80  
  7 purchase totals = $967.94       $1,048.1553   $1,048.15   $1,048.15   $1,048.30