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	$167.75	10.829%	$185.9156	$185.92	$185.90	$185.90
Purchase #2	$84.75	6.523%	$90.2782	$90.28	$90.30	$90.30
Purchase #3	$175.44	4.700%	$183.6857	$183.69	$183.70	$183.70
Purchase #4	$148.30	5.347%	$156.2296	$156.23	$156.25	$156.20
Purchase #5	$104.95	4.663%	$109.8438	$109.84	$109.85	$109.80
Purchase #6	$146.29	13.287%	$165.7276	$165.73	$165.75	$165.70
Purchase #7	$84.44	9.524%	$92.4821	$92.48	$92.50	$92.50
7 purchase totals =	$911.92		$984.1626	$984.17	$984.25	$984.10