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 $25.86   6.367%   $27.5065   $27.51   $27.50   $27.50  
  Purchase #2 $115.80   6.711%   $123.5713   $123.57   $123.55   $123.60  
  Purchase #3 $74.31   12.133%   $83.326   $83.33   $83.35   $83.30  
  Purchase #4 $58.66   4.106%   $61.0686   $61.07   $61.05   $61.10  
  Purchase #5 $54.79   6.522%   $58.3634   $58.36   $58.35   $58.40  
  Purchase #6 $122.45   3.153%   $126.3108   $126.31   $126.30   $126.30  
  Purchase #7 $235.93   7.445%   $253.495   $253.50   $253.50   $253.50  
  7 purchase totals = $687.80       $733.6416   $733.65   $733.60   $733.70