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	$46.73	6.682%	$49.8525	$49.85	$49.85	$49.90
Purchase #2	$219.74	4.371%	$229.3448	$229.34	$229.35	$229.30
Purchase #3	$231.93	4.797%	$243.0557	$243.06	$243.05	$243.10
Purchase #4	$95.28	13.240%	$107.8951	$107.90	$107.90	$107.90
Purchase #5	$48.55	8.191%	$52.5267	$52.53	$52.55	$52.50
Purchase #6	$79.48	3.556%	$82.3063	$82.31	$82.30	$82.30
Purchase #7	$40.27	12.627%	$45.3549	$45.35	$45.35	$45.40
7 purchase totals =	$761.98		$810.3360	$810.34	$810.35	$810.40