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 $192.67   7.202%   $206.5461   $206.55   $206.55   $206.50  
  Purchase #2 $155.78   10.377%   $171.9453   $171.95   $171.95   $171.90  
  Purchase #3 $134.49   6.330%   $143.0032   $143.00   $143.00   $143.00  
  Purchase #4 $83.82   4.615%   $87.6883   $87.69   $87.70   $87.70  
  Purchase #5 $86.96   8.292%   $94.1707   $94.17   $94.15   $94.20  
  Purchase #6 $8.56   12.158%   $9.6007   $9.60   $9.60   $9.60  
  Purchase #7 $31.67   11.770%   $35.3976   $35.40   $35.40   $35.40  
  7 purchase totals = $693.95       $748.3519   $748.36   $748.35   $748.30