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 $60.72   3.174%   $62.6473   $62.65   $62.65   $62.60  
  Purchase #2 $160.97   5.786%   $170.2837   $170.28   $170.30   $170.30  
  Purchase #3 $55.27   13.596%   $62.7845   $62.78   $62.80   $62.80  
  Purchase #4 $157.75   11.624%   $176.0869   $176.09   $176.10   $176.10  
  Purchase #5 $35.28   9.130%   $38.5011   $38.50   $38.50   $38.50  
  Purchase #6 $168.80   8.718%   $183.516   $183.52   $183.50   $183.50  
  Purchase #7 $59.31   10.829%   $65.7327   $65.73   $65.75   $65.70  
  7 purchase totals = $698.10       $759.5522   $759.55   $759.60   $759.50