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 $177.82   10.234%   $196.0181   $196.02   $196.00   $196.00  
  Purchase #2 $60.61   4.636%   $63.4199   $63.42   $63.40   $63.40  
  Purchase #3 $73.68   8.672%   $80.0695   $80.07   $80.05   $80.10  
  Purchase #4 $210.94   6.455%   $224.5562   $224.56   $224.55   $224.60  
  Purchase #5 $210.72   7.482%   $226.4861   $226.49   $226.50   $226.50  
  Purchase #6 $91.42   8.223%   $98.9375   $98.94   $98.95   $98.90  
  Purchase #7 $131.30   11.273%   $146.1014   $146.10   $146.10   $146.10  
  7 purchase totals = $956.49       $1,035.5887   $1,035.60   $1,035.55   $1,035.60