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 $111.41   6.143%   $118.2539   $118.25   $118.25   $118.30  
  Purchase #2 $217.43   7.549%   $233.8438   $233.84   $233.85   $233.80  
  Purchase #3 $143.93   8.548%   $156.2331   $156.23   $156.25   $156.20  
  Purchase #4 $56.43   12.658%   $63.5729   $63.57   $63.55   $63.60  
  Purchase #5 $11.26   12.485%   $12.6658   $12.67   $12.65   $12.70  
  Purchase #6 $232.64   10.655%   $257.4278   $257.43   $257.45   $257.40  
  Purchase #7 $12.81   9.685%   $14.0506   $14.05   $14.05   $14.10  
  7 purchase totals = $785.91       $856.0479   $856.04   $856.05   $856.10