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 $241.39   8.681%   $262.3451   $262.35   $262.35   $262.30  
  Purchase #2 $88.98   13.515%   $101.0056   $101.01   $101.00   $101.00  
  Purchase #3 $44.27   12.506%   $49.8064   $49.81   $49.80   $49.80  
  Purchase #4 $179.72   9.652%   $197.0666   $197.07   $197.05   $197.10  
  Purchase #5 $236.26   6.797%   $252.3186   $252.32   $252.30   $252.30  
  Purchase #6 $164.89   4.831%   $172.8558   $172.86   $172.85   $172.90  
  Purchase #7 $196.78   3.414%   $203.4981   $203.50   $203.50   $203.50  
  7 purchase totals = $1,152.29       $1,238.8962   $1,238.92   $1,238.85   $1,238.90