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 $61.61   5.139%   $64.7761   $64.78   $64.80   $64.80  
  Purchase #2 $157.34   11.187%   $174.9416   $174.94   $174.95   $174.90  
  Purchase #3 $185.94   11.316%   $206.981   $206.98   $207.00   $207.00  
  Purchase #4 $189.85   8.397%   $205.7917   $205.79   $205.80   $205.80  
  Purchase #5 $46.55   5.404%   $49.0656   $49.07   $49.05   $49.10  
  Purchase #6 $127.49   9.710%   $139.8693   $139.87   $139.85   $139.90  
  Purchase #7 $155.51   4.602%   $162.6666   $162.67   $162.65   $162.70  
  7 purchase totals = $924.29       $1,004.0919   $1,004.10   $1,004.10   $1,004.20