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	$28.47	12.621%	$32.0632	$32.06	$32.05	$32.10
Purchase #2	$202.68	7.364%	$217.6054	$217.61	$217.60	$217.60
Purchase #3	$82.60	11.508%	$92.1056	$92.11	$92.10	$92.10
Purchase #4	$156.35	9.636%	$171.4159	$171.42	$171.40	$171.40
Purchase #5	$39.62	3.319%	$40.935	$40.94	$40.95	$40.90
Purchase #6	$250.48	3.693%	$259.7302	$259.73	$259.75	$259.70
Purchase #7	$245.33	12.406%	$275.7656	$275.77	$275.75	$275.80
7 purchase totals =	$1,005.53		$1,089.6209	$1,089.64	$1,089.60	$1,089.60