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 $119.60   13.731%   $136.0223   $136.02   $136.00   $136.00  
  Purchase #2 $147.98   5.543%   $156.1825   $156.18   $156.20   $156.20  
  Purchase #3 $37.99   3.803%   $39.4348   $39.43   $39.45   $39.40  
  Purchase #4 $189.62   11.553%   $211.5268   $211.53   $211.55   $211.50  
  Purchase #5 $223.48   7.865%   $241.0567   $241.06   $241.05   $241.10  
  Purchase #6 $104.71   4.169%   $109.0754   $109.08   $109.10   $109.10  
  Purchase #7 $121.48   8.342%   $131.6139   $131.61   $131.60   $131.60  
  7 purchase totals = $944.86       $1,024.9124   $1,024.91   $1,024.95   $1,024.90