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 $87.84   12.339%   $98.6786   $98.68   $98.70   $98.70  
  Purchase #2 $234.82   4.591%   $245.6006   $245.60   $245.60   $245.60  
  Purchase #3 $197.25   12.229%   $221.3717   $221.37   $221.35   $221.40  
  Purchase #4 $41.44   5.845%   $43.8622   $43.86   $43.85   $43.90  
  Purchase #5 $111.65   9.529%   $122.2891   $122.29   $122.30   $122.30  
  Purchase #6 $212.86   5.459%   $224.48   $224.48   $224.50   $224.50  
  Purchase #7 $233.46   9.862%   $256.4838   $256.48   $256.50   $256.50  
  7 purchase totals = $1,119.32       $1,212.7660   $1,212.76   $1,212.80   $1,212.90