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 $38.98   11.371%   $43.4124   $43.41   $43.40   $43.40  
  Purchase #2 $183.51   11.708%   $204.9954   $205.00   $205.00   $205.00  
  Purchase #3 $113.47   10.180%   $125.0212   $125.02   $125.00   $125.00  
  Purchase #4 $69.85   7.308%   $74.9546   $74.95   $74.95   $75.00  
  Purchase #5 $77.73   11.166%   $86.4093   $86.41   $86.40   $86.40  
  Purchase #6 $119.83   3.703%   $124.2673   $124.27   $124.25   $124.30  
  Purchase #7 $186.34   12.476%   $209.5878   $209.59   $209.60   $209.60  
  7 purchase totals = $789.71       $868.6480   $868.65   $868.60   $868.70