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 $186.70   11.660%   $208.4692   $208.47   $208.45   $208.50  
  Purchase #2 $57.68   4.600%   $60.3333   $60.33   $60.35   $60.30  
  Purchase #3 $184.51   5.811%   $195.2319   $195.23   $195.25   $195.20  
  Purchase #4 $155.94   9.145%   $170.2007   $170.20   $170.20   $170.20  
  Purchase #5 $8.76   8.775%   $9.5287   $9.53   $9.55   $9.50  
  Purchase #6 $201.50   5.115%   $211.8067   $211.81   $211.80   $211.80  
  Purchase #7 $183.51   9.201%   $200.3948   $200.39   $200.40   $200.40  
  7 purchase totals = $978.60       $1,055.9653   $1,055.96   $1,056.00   $1,055.90