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	$84.34	5.594%	$89.058	$89.06	$89.05	$89.10
Purchase #2	$7.70	4.777%	$8.0678	$8.07	$8.05	$8.10
Purchase #3	$215.49	11.771%	$240.8553	$240.86	$240.85	$240.90
Purchase #4	$140.33	3.698%	$145.5194	$145.52	$145.50	$145.50
Purchase #5	$221.92	8.538%	$240.8675	$240.87	$240.85	$240.90
Purchase #6	$79.51	9.319%	$86.9195	$86.92	$86.90	$86.90
Purchase #7	$230.47	5.791%	$243.8165	$243.82	$243.80	$243.80
7 purchase totals =	$979.76		$1,055.1040	$1,055.12	$1,055.00	$1,055.20