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	$71.56	13.792%	$81.4296	$81.43	$81.45	$81.40
Purchase #2	$76.56	9.573%	$83.8891	$83.89	$83.90	$83.90
Purchase #3	$68.92	3.562%	$71.3749	$71.37	$71.35	$71.40
Purchase #4	$48.40	6.180%	$51.3911	$51.39	$51.40	$51.40
Purchase #5	$222.46	8.134%	$240.5549	$240.55	$240.55	$240.60
Purchase #6	$46.44	10.494%	$51.3134	$51.31	$51.30	$51.30
Purchase #7	$248.33	9.340%	$271.524	$271.52	$271.50	$271.50
7 purchase totals =	$782.67		$851.4770	$851.46	$851.45	$851.50