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	$157.98	4.759%	$165.4983	$165.50	$165.50	$165.50
Purchase #2	$22.43	9.560%	$24.5743	$24.57	$24.55	$24.60
Purchase #3	$60.56	11.869%	$67.7479	$67.75	$67.75	$67.70
Purchase #4	$84.74	6.399%	$90.1625	$90.16	$90.15	$90.20
Purchase #5	$177.51	10.490%	$196.1308	$196.13	$196.15	$196.10
Purchase #6	$51.72	8.320%	$56.0231	$56.02	$56.00	$56.00
Purchase #7	$184.82	3.806%	$191.8542	$191.85	$191.85	$191.90
7 purchase totals =	$739.76		$791.9911	$791.98	$791.95	$792.00