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 $245.80   5.206%   $258.5963   $258.60   $258.60   $258.60  
  Purchase #2 $54.80   4.732%   $57.3931   $57.39   $57.40   $57.40  
  Purchase #3 $123.66   3.187%   $127.601   $127.60   $127.60   $127.60  
  Purchase #4 $71.64   3.663%   $74.2642   $74.26   $74.25   $74.30  
  Purchase #5 $168.64   5.659%   $178.1833   $178.18   $178.20   $178.20  
  Purchase #6 $175.66   7.853%   $189.4546   $189.45   $189.45   $189.50  
  Purchase #7 $22.72   7.711%   $24.4719   $24.47   $24.45   $24.50  
  7 purchase totals = $862.92       $909.9644   $909.95   $909.95   $910.10