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 $182.85   12.767%   $206.1945   $206.19   $206.20   $206.20  
  Purchase #2 $243.81   6.740%   $260.2428   $260.24   $260.25   $260.20  
  Purchase #3 $13.50   13.178%   $15.279   $15.28   $15.30   $15.30  
  Purchase #4 $20.41   12.607%   $22.9831   $22.98   $23.00   $23.00  
  Purchase #5 $54.55   6.725%   $58.2185   $58.22   $58.20   $58.20  
  Purchase #6 $249.37   5.731%   $263.6614   $263.66   $263.65   $263.70  
  Purchase #7 $222.65   8.253%   $241.0253   $241.03   $241.05   $241.00  
  7 purchase totals = $987.14       $1,067.6046   $1,067.60   $1,067.65   $1,067.60