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 $158.47   5.872%   $167.7754   $167.78   $167.80   $167.80  
  Purchase #2 $179.33   10.778%   $198.6582   $198.66   $198.65   $198.70  
  Purchase #3 $164.56   13.391%   $186.5962   $186.60   $186.60   $186.60  
  Purchase #4 $130.57   3.692%   $135.3906   $135.39   $135.40   $135.40  
  Purchase #5 $61.53   12.558%   $69.2569   $69.26   $69.25   $69.30  
  Purchase #6 $216.27   3.807%   $224.5034   $224.50   $224.50   $224.50  
  Purchase #7 $20.49   3.665%   $21.241   $21.24   $21.25   $21.20  
  7 purchase totals = $931.22       $1,003.4217   $1,003.43   $1,003.45   $1,003.50