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 $168.54   13.379%   $191.089   $191.09   $191.10   $191.10  
  Purchase #2 $118.33   11.527%   $131.9699   $131.97   $131.95   $132.00  
  Purchase #3 $245.47   4.176%   $255.7208   $255.72   $255.70   $255.70  
  Purchase #4 $214.44   13.355%   $243.0785   $243.08   $243.10   $243.10  
  Purchase #5 $209.76   4.659%   $219.5327   $219.53   $219.55   $219.50  
  Purchase #6 $110.58   12.746%   $124.6745   $124.67   $124.65   $124.70  
  Purchase #7 $192.58   8.104%   $208.1867   $208.19   $208.20   $208.20  
  7 purchase totals = $1,259.70       $1,374.2521   $1,374.25   $1,374.25   $1,374.30