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 $119.50   4.597%   $124.9934   $124.99   $125.00   $125.00  
  Purchase #2 $235.98   12.446%   $265.3501   $265.35   $265.35   $265.40  
  Purchase #3 $45.52   8.527%   $49.4015   $49.40   $49.40   $49.40  
  Purchase #4 $80.59   3.397%   $83.3276   $83.33   $83.35   $83.30  
  Purchase #5 $230.47   12.647%   $259.6175   $259.62   $259.60   $259.60  
  Purchase #6 $199.61   13.231%   $226.0204   $226.02   $226.00   $226.00  
  Purchase #7 $117.44   11.248%   $130.6497   $130.65   $130.65   $130.60  
  7 purchase totals = $1,029.11       $1,139.3602   $1,139.36   $1,139.35   $1,139.30