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 $91.77   3.809%   $95.2655   $95.27   $95.25   $95.30  
  Purchase #2 $233.35   11.551%   $260.3043   $260.30   $260.30   $260.30  
  Purchase #3 $94.51   5.755%   $99.9491   $99.95   $99.95   $99.90  
  Purchase #4 $220.48   12.241%   $247.469   $247.47   $247.45   $247.50  
  Purchase #5 $188.56   13.584%   $214.174   $214.17   $214.15   $214.20  
  Purchase #6 $114.49   9.228%   $125.0551   $125.06   $125.05   $125.10  
  Purchase #7 $120.87   8.646%   $131.3204   $131.32   $131.30   $131.30  
  7 purchase totals = $1,064.03       $1,173.5374   $1,173.54   $1,173.45   $1,173.60