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 $224.95   12.777%   $253.6919   $253.69   $253.70   $253.70  
  Purchase #2 $90.99   13.668%   $103.4265   $103.43   $103.45   $103.40  
  Purchase #3 $93.74   4.770%   $98.2114   $98.21   $98.20   $98.20  
  Purchase #4 $136.47   6.740%   $145.6681   $145.67   $145.65   $145.70  
  Purchase #5 $67.74   12.801%   $76.4114   $76.41   $76.40   $76.40  
  Purchase #6 $233.93   4.843%   $245.2592   $245.26   $245.25   $245.30  
  Purchase #7 $122.78   11.309%   $136.6652   $136.67   $136.65   $136.70  
  7 purchase totals = $970.60       $1,059.3337   $1,059.34   $1,059.30   $1,059.40