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 $59.80   8.751%   $65.0331   $65.03   $65.05   $65.00  
  Purchase #2 $214.74   8.665%   $233.3472   $233.35   $233.35   $233.30  
  Purchase #3 $124.29   10.143%   $136.8967   $136.90   $136.90   $136.90  
  Purchase #4 $247.59   7.250%   $265.5403   $265.54   $265.55   $265.50  
  Purchase #5 $30.51   6.746%   $32.5682   $32.57   $32.55   $32.60  
  Purchase #6 $186.47   10.846%   $206.6945   $206.69   $206.70   $206.70  
  Purchase #7 $78.25   12.666%   $88.1611   $88.16   $88.15   $88.20  
  7 purchase totals = $941.65       $1,028.2411   $1,028.24   $1,028.25   $1,028.20