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 $73.88   3.497%   $76.4636   $76.46   $76.45   $76.50  
  Purchase #2 $7.99   9.511%   $8.7499   $8.75   $8.75   $8.70  
  Purchase #3 $196.27   6.226%   $208.4898   $208.49   $208.50   $208.50  
  Purchase #4 $91.99   6.870%   $98.3097   $98.31   $98.30   $98.30  
  Purchase #5 $179.69   9.717%   $197.1505   $197.15   $197.15   $197.20  
  Purchase #6 $246.94   4.619%   $258.3462   $258.35   $258.35   $258.30  
  Purchase #7 $184.77   9.216%   $201.7984   $201.80   $201.80   $201.80  
  7 purchase totals = $981.53       $1,049.3081   $1,049.31   $1,049.30   $1,049.30