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 $246.87   10.268%   $272.2186   $272.22   $272.20   $272.20  
  Purchase #2 $107.80   13.778%   $122.6527   $122.65   $122.65   $122.70  
  Purchase #3 $86.58   13.435%   $98.212   $98.21   $98.20   $98.20  
  Purchase #4 $69.53   11.250%   $77.3521   $77.35   $77.35   $77.40  
  Purchase #5 $74.95   9.272%   $81.8994   $81.90   $81.90   $81.90  
  Purchase #6 $140.75   7.714%   $151.6075   $151.61   $151.60   $151.60  
  Purchase #7 $51.66   5.841%   $54.6775   $54.68   $54.70   $54.70  
  7 purchase totals = $778.14       $858.6198   $858.62   $858.60   $858.70