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	$123.78	7.562%	$133.1402	$133.14	$133.15	$133.10
Purchase #2	$152.68	9.680%	$167.4594	$167.46	$167.45	$167.50
Purchase #3	$179.86	9.450%	$196.8568	$196.86	$196.85	$196.90
Purchase #4	$113.90	13.234%	$128.9735	$128.97	$128.95	$129.00
Purchase #5	$242.48	6.734%	$258.8086	$258.81	$258.80	$258.80
Purchase #6	$6.62	10.391%	$7.3079	$7.31	$7.30	$7.30
Purchase #7	$47.34	5.692%	$50.0346	$50.03	$50.05	$50.00
7 purchase totals =	$866.66		$942.5810	$942.58	$942.55	$942.60