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	$220.98	6.578%	$235.5161	$235.52	$235.50	$235.50
Purchase #2	$38.40	11.761%	$42.9162	$42.92	$42.90	$42.90
Purchase #3	$216.56	3.330%	$223.7714	$223.77	$223.75	$223.80
Purchase #4	$59.85	8.445%	$64.9043	$64.90	$64.90	$64.90
Purchase #5	$135.77	8.117%	$146.7905	$146.79	$146.80	$146.80
Purchase #6	$90.32	11.533%	$100.7366	$100.74	$100.75	$100.70
Purchase #7	$62.42	3.588%	$64.6596	$64.66	$64.65	$64.70
7 purchase totals =	$824.30		$879.2947	$879.30	$879.25	$879.30