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 $53.85   13.685%   $61.2194   $61.22   $61.20   $61.20  
  Purchase #2 $217.59   13.368%   $246.6774   $246.68   $246.70   $246.70  
  Purchase #3 $201.46   5.495%   $212.5302   $212.53   $212.55   $212.50  
  Purchase #4 $170.38   4.768%   $178.5037   $178.50   $178.50   $178.50  
  Purchase #5 $229.90   13.686%   $261.3641   $261.36   $261.35   $261.40  
  Purchase #6 $172.37   12.103%   $193.2319   $193.23   $193.25   $193.20  
  Purchase #7 $160.49   11.518%   $178.9752   $178.98   $179.00   $179.00  
  7 purchase totals = $1,206.04       $1,332.5019   $1,332.50   $1,332.55   $1,332.50