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	$79.81	12.278%	$89.6091	$89.61	$89.60	$89.60
Purchase #2	$16.27	12.336%	$18.2771	$18.28	$18.30	$18.30
Purchase #3	$88.68	9.289%	$96.9175	$96.92	$96.90	$96.90
Purchase #4	$235.89	6.213%	$250.5458	$250.55	$250.55	$250.50
Purchase #5	$114.47	12.292%	$128.5407	$128.54	$128.55	$128.50
Purchase #6	$37.47	7.264%	$40.1918	$40.19	$40.20	$40.20
Purchase #7	$131.87	3.102%	$135.9606	$135.96	$135.95	$136.00
7 purchase totals =	$704.46		$760.0426	$760.05	$760.05	$760.00