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	$34.72	7.121%	$37.1924	$37.19	$37.20	$37.20
Purchase #2	$200.90	8.251%	$217.4763	$217.48	$217.50	$217.50
Purchase #3	$187.29	4.663%	$196.0233	$196.02	$196.00	$196.00
Purchase #4	$239.30	12.454%	$269.1024	$269.10	$269.10	$269.10
Purchase #5	$59.76	7.839%	$64.4446	$64.44	$64.45	$64.40
Purchase #6	$115.59	12.357%	$129.8735	$129.87	$129.85	$129.90
Purchase #7	$57.97	10.689%	$64.1664	$64.17	$64.15	$64.20
7 purchase totals =	$895.53		$978.2789	$978.27	$978.25	$978.30