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 $64.47   4.484%   $67.3608   $67.36   $67.35   $67.40  
  Purchase #2 $129.82   5.448%   $136.8926   $136.89   $136.90   $136.90  
  Purchase #3 $244.52   9.476%   $267.6907   $267.69   $267.70   $267.70  
  Purchase #4 $235.88   6.381%   $250.9315   $250.93   $250.95   $250.90  
  Purchase #5 $234.42   11.856%   $262.2128   $262.21   $262.20   $262.20  
  Purchase #6 $222.90   13.301%   $252.5479   $252.55   $252.55   $252.50  
  Purchase #7 $22.92   12.370%   $25.7552   $25.76   $25.75   $25.80  
  7 purchase totals = $1,154.93       $1,263.3915   $1,263.39   $1,263.40   $1,263.40