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 $50.53   8.216%   $54.6815   $54.68   $54.70   $54.70  
  Purchase #2 $171.70   4.778%   $179.9038   $179.90   $179.90   $179.90  
  Purchase #3 $215.30   4.618%   $225.2426   $225.24   $225.25   $225.20  
  Purchase #4 $46.80   12.415%   $52.6102   $52.61   $52.60   $52.60  
  Purchase #5 $208.63   11.113%   $231.8151   $231.82   $231.80   $231.80  
  Purchase #6 $230.27   8.556%   $249.9719   $249.97   $249.95   $250.00  
  Purchase #7 $201.51   3.416%   $208.3936   $208.39   $208.40   $208.40  
  7 purchase totals = $1,124.74       $1,202.6187   $1,202.61   $1,202.60   $1,202.60