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 $118.72   6.260%   $126.1519   $126.15   $126.15   $126.20  
  Purchase #2 $167.60   9.183%   $182.9907   $182.99   $183.00   $183.00  
  Purchase #3 $24.65   10.530%   $27.2456   $27.25   $27.25   $27.20  
  Purchase #4 $51.83   11.517%   $57.7993   $57.80   $57.80   $57.80  
  Purchase #5 $182.96   6.264%   $194.4206   $194.42   $194.40   $194.40  
  Purchase #6 $84.65   13.311%   $95.9178   $95.92   $95.90   $95.90  
  Purchase #7 $115.46   3.835%   $119.8879   $119.89   $119.90   $119.90  
  7 purchase totals = $745.87       $804.4138   $804.42   $804.40   $804.40