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 $56.57   13.526%   $64.2217   $64.22   $64.20   $64.20  
  Purchase #2 $215.52   10.560%   $238.2789   $238.28   $238.30   $238.30  
  Purchase #3 $124.76   7.605%   $134.248   $134.25   $134.25   $134.20  
  Purchase #4 $49.64   10.273%   $54.7395   $54.74   $54.75   $54.70  
  Purchase #5 $247.53   9.645%   $271.4043   $271.40   $271.40   $271.40  
  Purchase #6 $126.74   8.469%   $137.4736   $137.47   $137.45   $137.50  
  Purchase #7 $138.93   7.207%   $148.9427   $148.94   $148.95   $148.90  
  7 purchase totals = $959.69       $1,049.3087   $1,049.30   $1,049.30   $1,049.20