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	$101.28	10.321%	$111.7331	$111.73	$111.75	$111.70
Purchase #2	$117.40	5.799%	$124.208	$124.21	$124.20	$124.20
Purchase #3	$199.87	11.585%	$223.0249	$223.02	$223.00	$223.00
Purchase #4	$51.61	6.355%	$54.8898	$54.89	$54.90	$54.90
Purchase #5	$35.48	11.286%	$39.4843	$39.48	$39.50	$39.50
Purchase #6	$142.53	9.774%	$156.4609	$156.46	$156.45	$156.50
Purchase #7	$198.91	9.760%	$218.3236	$218.32	$218.30	$218.30
7 purchase totals =	$847.08		$928.1246	$928.11	$928.10	$928.10