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	$35.78	4.689%	$37.4577	$37.46	$37.45	$37.50
Purchase #2	$95.75	5.430%	$100.9492	$100.95	$100.95	$100.90
Purchase #3	$120.81	4.162%	$125.8381	$125.84	$125.85	$125.80
Purchase #4	$100.69	5.632%	$106.3609	$106.36	$106.35	$106.40
Purchase #5	$18.91	10.541%	$20.9033	$20.90	$20.90	$20.90
Purchase #6	$201.86	8.705%	$219.4319	$219.43	$219.45	$219.40
Purchase #7	$209.63	8.469%	$227.3836	$227.38	$227.40	$227.40
7 purchase totals =	$783.43		$838.3247	$838.32	$838.35	$838.30