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 $65.34   5.775%   $69.1134   $69.11   $69.10   $69.10  
  Purchase #2 $207.53   10.621%   $229.5718   $229.57   $229.55   $229.60  
  Purchase #3 $244.61   3.301%   $252.6846   $252.68   $252.70   $252.70  
  Purchase #4 $77.35   11.134%   $85.9621   $85.96   $85.95   $86.00  
  Purchase #5 $147.39   5.859%   $156.0256   $156.03   $156.05   $156.00  
  Purchase #6 $60.82   4.763%   $63.7169   $63.72   $63.70   $63.70  
  Purchase #7 $73.61   6.370%   $78.299   $78.30   $78.30   $78.30  
  7 purchase totals = $876.65       $935.3734   $935.37   $935.35   $935.40