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 $24.61   6.677%   $26.2532   $26.25   $26.25   $26.30  
  Purchase #2 $174.57   11.704%   $195.0017   $195.00   $195.00   $195.00  
  Purchase #3 $128.35   6.717%   $136.9713   $136.97   $136.95   $137.00  
  Purchase #4 $232.98   10.739%   $257.9997   $258.00   $258.00   $258.00  
  Purchase #5 $155.59   13.684%   $176.8809   $176.88   $176.90   $176.90  
  Purchase #6 $79.70   7.147%   $85.3962   $85.40   $85.40   $85.40  
  Purchase #7 $52.56   5.635%   $55.5218   $55.52   $55.50   $55.50  
  7 purchase totals = $848.36       $934.0248   $934.02   $934.00   $934.10