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	$28.67	11.647%	$32.0092	$32.01	$32.00	$32.00
Purchase #2	$98.97	12.483%	$111.3244	$111.32	$111.30	$111.30
Purchase #3	$216.58	7.337%	$232.4705	$232.47	$232.45	$232.50
Purchase #4	$216.46	12.306%	$243.0976	$243.10	$243.10	$243.10
Purchase #5	$67.92	6.505%	$72.3382	$72.34	$72.35	$72.30
Purchase #6	$239.83	8.153%	$259.3833	$259.38	$259.40	$259.40
Purchase #7	$211.89	8.109%	$229.0722	$229.07	$229.05	$229.10
7 purchase totals =	$1,080.32		$1,179.6954	$1,179.69	$1,179.65	$1,179.70