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 $119.66   6.240%   $127.1268   $127.13   $127.15   $127.10  
  Purchase #2 $70.81   6.279%   $75.2562   $75.26   $75.25   $75.30  
  Purchase #3 $117.80   6.178%   $125.0777   $125.08   $125.10   $125.10  
  Purchase #4 $217.38   4.560%   $227.2925   $227.29   $227.30   $227.30  
  Purchase #5 $56.91   8.639%   $61.8265   $61.83   $61.85   $61.80  
  Purchase #6 $75.36   9.430%   $82.4664   $82.47   $82.45   $82.50  
  Purchase #7 $181.54   7.503%   $195.1609   $195.16   $195.15   $195.20  
  7 purchase totals = $839.46       $894.2070   $894.22   $894.25   $894.30