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	$247.61	4.796%	$259.4854	$259.49	$259.50	$259.50
Purchase #2	$93.58	7.741%	$100.824	$100.82	$100.80	$100.80
Purchase #3	$121.65	6.765%	$129.8796	$129.88	$129.90	$129.90
Purchase #4	$147.63	10.107%	$162.551	$162.55	$162.55	$162.60
Purchase #5	$43.36	5.562%	$45.7717	$45.77	$45.75	$45.80
Purchase #6	$106.92	10.793%	$118.4599	$118.46	$118.45	$118.50
Purchase #7	$59.48	12.804%	$67.0958	$67.10	$67.10	$67.10
7 purchase totals =	$820.23		$884.0674	$884.07	$884.05	$884.20