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	$241.56	5.253%	$254.2491	$254.25	$254.25	$254.20
Purchase #2	$104.50	7.700%	$112.5465	$112.55	$112.55	$112.50
Purchase #3	$211.58	10.818%	$234.4687	$234.47	$234.45	$234.50
Purchase #4	$223.94	9.155%	$244.4417	$244.44	$244.45	$244.40
Purchase #5	$183.42	6.121%	$194.6471	$194.65	$194.65	$194.60
Purchase #6	$73.36	12.421%	$82.472	$82.47	$82.45	$82.50
Purchase #7	$83.51	6.798%	$89.187	$89.19	$89.20	$89.20
7 purchase totals =	$1,121.87		$1,212.0121	$1,212.02	$1,212.00	$1,211.90