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 $55.76   13.547%   $63.3138   $63.31   $63.30   $63.30  
  Purchase #2 $230.99   6.780%   $246.6511   $246.65   $246.65   $246.70  
  Purchase #3 $54.79   4.412%   $57.2073   $57.21   $57.20   $57.20  
  Purchase #4 $111.35   11.439%   $124.0873   $124.09   $124.10   $124.10  
  Purchase #5 $129.44   13.458%   $146.86   $146.86   $146.85   $146.90  
  Purchase #6 $140.35   6.125%   $148.9464   $148.95   $148.95   $148.90  
  Purchase #7 $53.65   5.215%   $56.4478   $56.45   $56.45   $56.40  
  7 purchase totals = $776.33       $843.5137   $843.52   $843.50   $843.50