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 $158.97   11.846%   $177.8016   $177.80   $177.80   $177.80  
  Purchase #2 $216.67   10.358%   $239.1127   $239.11   $239.10   $239.10  
  Purchase #3 $73.76   13.742%   $83.8961   $83.90   $83.90   $83.90  
  Purchase #4 $22.56   4.577%   $23.5926   $23.59   $23.60   $23.60  
  Purchase #5 $97.94   11.318%   $109.0248   $109.02   $109.00   $109.00  
  Purchase #6 $135.85   12.403%   $152.6995   $152.70   $152.70   $152.70  
  Purchase #7 $221.47   5.394%   $233.4161   $233.42   $233.40   $233.40  
  7 purchase totals = $927.22       $1,019.5434   $1,019.54   $1,019.50   $1,019.50