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	$223.42	12.285%	$250.8671	$250.87	$250.85	$250.90
Purchase #2	$61.96	12.109%	$69.4627	$69.46	$69.45	$69.50
Purchase #3	$26.48	4.288%	$27.6155	$27.62	$27.60	$27.60
Purchase #4	$104.43	11.399%	$116.334	$116.33	$116.35	$116.30
Purchase #5	$53.81	5.302%	$56.663	$56.66	$56.65	$56.70
Purchase #6	$55.42	13.556%	$62.9327	$62.93	$62.95	$62.90
Purchase #7	$168.72	3.307%	$174.2996	$174.30	$174.30	$174.30
7 purchase totals =	$694.24		$758.1746	$758.17	$758.15	$758.20