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 $53.97   8.801%   $58.7199   $58.72   $58.70   $58.70  
  Purchase #2 $90.38   5.806%   $95.6275   $95.63   $95.65   $95.60  
  Purchase #3 $245.55   3.782%   $254.8367   $254.84   $254.85   $254.80  
  Purchase #4 $179.56   9.636%   $196.8624   $196.86   $196.85   $196.90  
  Purchase #5 $227.30   8.537%   $246.7046   $246.70   $246.70   $246.70  
  Purchase #6 $227.53   3.575%   $235.6642   $235.66   $235.65   $235.70  
  Purchase #7 $199.82   3.203%   $206.2202   $206.22   $206.20   $206.20  
  7 purchase totals = $1,224.11       $1,294.6355   $1,294.63   $1,294.60   $1,294.60