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 $55.47   5.561%   $58.5547   $58.55   $58.55   $58.60  
  Purchase #2 $117.26   6.585%   $124.9816   $124.98   $125.00   $125.00  
  Purchase #3 $104.72   9.446%   $114.6119   $114.61   $114.60   $114.60  
  Purchase #4 $224.71   3.477%   $232.5232   $232.52   $232.50   $232.50  
  Purchase #5 $210.74   12.386%   $236.8423   $236.84   $236.85   $236.80  
  Purchase #6 $180.83   3.140%   $186.5081   $186.51   $186.50   $186.50  
  Purchase #7 $5.37   11.560%   $5.9908   $5.99   $6.00   $6.00  
  7 purchase totals = $899.10       $960.0126   $960.00   $960.00   $960.00