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	$81.43	12.851%	$91.8946	$91.89	$91.90	$91.90
Purchase #2	$100.62	10.619%	$111.3048	$111.30	$111.30	$111.30
Purchase #3	$247.33	12.555%	$278.3823	$278.38	$278.40	$278.40
Purchase #4	$84.96	9.399%	$92.9454	$92.95	$92.95	$92.90
Purchase #5	$250.39	5.166%	$263.3251	$263.33	$263.35	$263.30
Purchase #6	$85.59	3.499%	$88.5848	$88.58	$88.60	$88.60
Purchase #7	$202.87	9.503%	$222.1487	$222.15	$222.15	$222.10
7 purchase totals =	$1,053.19		$1,148.5857	$1,148.58	$1,148.65	$1,148.50