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 $249.90   13.464%   $283.5465   $283.55   $283.55   $283.50  
  Purchase #2 $23.78   3.495%   $24.6111   $24.61   $24.60   $24.60  
  Purchase #3 $229.93   9.742%   $252.3298   $252.33   $252.35   $252.30  
  Purchase #4 $11.25   3.111%   $11.6   $11.60   $11.60   $11.60  
  Purchase #5 $168.64   5.520%   $177.9489   $177.95   $177.95   $177.90  
  Purchase #6 $181.47   5.607%   $191.645   $191.65   $191.65   $191.60  
  Purchase #7 $68.66   4.133%   $71.4977   $71.50   $71.50   $71.50  
  7 purchase totals = $933.63       $1,013.1790   $1,013.19   $1,013.20   $1,013.00