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	$72.90	10.146%	$80.2964	$80.30	$80.30	$80.30
Purchase #2	$232.74	3.169%	$240.1155	$240.12	$240.10	$240.10
Purchase #3	$77.44	10.799%	$85.8027	$85.80	$85.80	$85.80
Purchase #4	$83.44	7.729%	$89.8891	$89.89	$89.90	$89.90
Purchase #5	$171.30	8.453%	$185.78	$185.78	$185.80	$185.80
Purchase #6	$37.93	10.566%	$41.9377	$41.94	$41.95	$41.90
Purchase #7	$8.41	10.198%	$9.2677	$9.27	$9.25	$9.30
7 purchase totals =	$684.16		$733.0891	$733.10	$733.10	$733.10