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 $61.40   8.519%   $66.6307   $66.63   $66.65   $66.60  
  Purchase #2 $100.34   13.767%   $114.1538   $114.15   $114.15   $114.20  
  Purchase #3 $61.47   8.369%   $66.6144   $66.61   $66.60   $66.60  
  Purchase #4 $201.58   7.188%   $216.0696   $216.07   $216.05   $216.10  
  Purchase #5 $224.30   12.570%   $252.4945   $252.49   $252.50   $252.50  
  Purchase #6 $246.26   11.820%   $275.3679   $275.37   $275.35   $275.40  
  Purchase #7 $186.67   12.852%   $210.6608   $210.66   $210.65   $210.70  
  7 purchase totals = $1,082.02       $1,201.9917   $1,201.98   $1,201.95   $1,202.10