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	$84.97	5.601%	$89.7292	$89.73	$89.75	$89.70
Purchase #2	$229.33	9.311%	$250.6829	$250.68	$250.70	$250.70
Purchase #3	$70.30	12.321%	$78.9617	$78.96	$78.95	$79.00
Purchase #4	$14.27	3.626%	$14.7874	$14.79	$14.80	$14.80
Purchase #5	$91.98	13.363%	$104.2713	$104.27	$104.25	$104.30
Purchase #6	$48.76	7.282%	$52.3107	$52.31	$52.30	$52.30
Purchase #7	$148.64	12.553%	$167.2988	$167.30	$167.30	$167.30
7 purchase totals =	$688.25		$758.0420	$758.04	$758.05	$758.10