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	$91.31	10.387%	$100.7944	$100.79	$100.80	$100.80
Purchase #2	$55.42	8.481%	$60.1202	$60.12	$60.10	$60.10
Purchase #3	$194.96	9.409%	$213.3038	$213.30	$213.30	$213.30
Purchase #4	$232.45	11.555%	$259.3096	$259.31	$259.30	$259.30
Purchase #5	$200.48	9.511%	$219.5477	$219.55	$219.55	$219.50
Purchase #6	$77.49	11.222%	$86.1859	$86.19	$86.20	$86.20
Purchase #7	$96.76	3.683%	$100.3237	$100.32	$100.30	$100.30
7 purchase totals =	$948.87		$1,039.5853	$1,039.58	$1,039.55	$1,039.50