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	$17.43	4.144%	$18.1523	$18.15	$18.15	$18.20
Purchase #2	$245.47	11.282%	$273.1639	$273.16	$273.15	$273.20
Purchase #3	$229.47	13.710%	$260.9303	$260.93	$260.95	$260.90
Purchase #4	$249.28	5.767%	$263.656	$263.66	$263.65	$263.70
Purchase #5	$53.64	11.444%	$59.7786	$59.78	$59.80	$59.80
Purchase #6	$126.37	8.500%	$137.1115	$137.11	$137.10	$137.10
Purchase #7	$70.65	11.865%	$79.0326	$79.03	$79.05	$79.00
7 purchase totals =	$992.31		$1,091.8252	$1,091.82	$1,091.85	$1,091.90