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 $246.92   5.187%   $259.7277   $259.73   $259.75   $259.70  
  Purchase #2 $186.51   6.477%   $198.5903   $198.59   $198.60   $198.60  
  Purchase #3 $87.30   7.412%   $93.7707   $93.77   $93.75   $93.80  
  Purchase #4 $201.88   6.164%   $214.3239   $214.32   $214.30   $214.30  
  Purchase #5 $113.74   6.230%   $120.826   $120.83   $120.85   $120.80  
  Purchase #6 $189.94   3.854%   $197.2603   $197.26   $197.25   $197.30  
  Purchase #7 $240.73   9.182%   $262.8338   $262.83   $262.85   $262.80  
  7 purchase totals = $1,267.02       $1,347.3327   $1,347.33   $1,347.35   $1,347.30