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 $86.41   9.459%   $94.5835   $94.58   $94.60   $94.60  
  Purchase #2 $68.65   12.626%   $77.3177   $77.32   $77.30   $77.30  
  Purchase #3 $17.33   7.195%   $18.5769   $18.58   $18.60   $18.60  
  Purchase #4 $166.93   4.515%   $174.4669   $174.47   $174.45   $174.50  
  Purchase #5 $170.73   7.729%   $183.9257   $183.93   $183.95   $183.90  
  Purchase #6 $164.94   7.464%   $177.2511   $177.25   $177.25   $177.30  
  Purchase #7 $206.30   13.221%   $233.5749   $233.57   $233.55   $233.60  
  7 purchase totals = $881.29       $959.6967   $959.70   $959.70   $959.80