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 $118.61   5.445%   $125.0683   $125.07   $125.05   $125.10  
  Purchase #2 $203.49   11.506%   $226.9036   $226.90   $226.90   $226.90  
  Purchase #3 $51.83   10.658%   $57.354   $57.35   $57.35   $57.40  
  Purchase #4 $167.80   9.680%   $184.043   $184.04   $184.05   $184.00  
  Purchase #5 $55.93   10.273%   $61.6757   $61.68   $61.70   $61.70  
  Purchase #6 $62.74   4.365%   $65.4786   $65.48   $65.50   $65.50  
  Purchase #7 $205.93   6.216%   $218.7306   $218.73   $218.75   $218.70  
  7 purchase totals = $866.33       $939.2538   $939.25   $939.30   $939.30