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 $54.25   11.707%   $60.601   $60.60   $60.60   $60.60  
  Purchase #2 $34.99   9.723%   $38.3921   $38.39   $38.40   $38.40  
  Purchase #3 $152.98   13.541%   $173.695   $173.70   $173.70   $173.70  
  Purchase #4 $96.93   11.137%   $107.7251   $107.73   $107.75   $107.70  
  Purchase #5 $40.96   6.794%   $43.7428   $43.74   $43.75   $43.70  
  Purchase #6 $88.67   7.248%   $95.0968   $95.10   $95.10   $95.10  
  Purchase #7 $216.32   6.697%   $230.807   $230.81   $230.80   $230.80  
  7 purchase totals = $685.10       $750.0598   $750.07   $750.10   $750.00