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	$93.99	6.515%	$100.1134	$100.11	$100.10	$100.10
Purchase #2	$144.52	5.353%	$152.2562	$152.26	$152.25	$152.30
Purchase #3	$90.34	9.582%	$98.9964	$99.00	$99.00	$99.00
Purchase #4	$39.27	6.790%	$41.9364	$41.94	$41.95	$41.90
Purchase #5	$189.48	8.583%	$205.7431	$205.74	$205.75	$205.70
Purchase #6	$159.50	6.116%	$169.255	$169.26	$169.25	$169.30
Purchase #7	$83.94	7.429%	$90.1759	$90.18	$90.20	$90.20
7 purchase totals =	$801.04		$858.4764	$858.49	$858.50	$858.50