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 $55.48   6.755%   $59.2277   $59.23   $59.25   $59.20  
  Purchase #2 $30.60   10.116%   $33.6955   $33.70   $33.70   $33.70  
  Purchase #3 $237.58   6.521%   $253.0726   $253.07   $253.05   $253.10  
  Purchase #4 $20.96   8.197%   $22.6781   $22.68   $22.70   $22.70  
  Purchase #5 $147.50   4.309%   $153.8558   $153.86   $153.85   $153.90  
  Purchase #6 $74.26   3.250%   $76.6735   $76.67   $76.65   $76.70  
  Purchase #7 $245.25   12.788%   $276.6126   $276.61   $276.60   $276.60  
  7 purchase totals = $811.63       $875.8158   $875.82   $875.80   $875.90