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 $201.34   3.652%   $208.6929   $208.69   $208.70   $208.70  
  Purchase #2 $65.97   6.601%   $70.3247   $70.32   $70.30   $70.30  
  Purchase #3 $172.36   6.635%   $183.7961   $183.80   $183.80   $183.80  
  Purchase #4 $123.35   7.377%   $132.4495   $132.45   $132.45   $132.40  
  Purchase #5 $87.60   4.218%   $91.295   $91.30   $91.30   $91.30  
  Purchase #6 $160.40   7.156%   $171.8782   $171.88   $171.90   $171.90  
  Purchase #7 $98.95   6.179%   $105.0641   $105.06   $105.05   $105.10  
  7 purchase totals = $909.97       $963.5005   $963.50   $963.50   $963.50