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	$6.42	3.107%	$6.6195	$6.62	$6.60	$6.60
Purchase #2	$247.43	10.379%	$273.1108	$273.11	$273.10	$273.10
Purchase #3	$233.86	3.199%	$241.3412	$241.34	$241.35	$241.30
Purchase #4	$216.69	12.787%	$244.3982	$244.40	$244.40	$244.40
Purchase #5	$216.40	3.462%	$223.8918	$223.89	$223.90	$223.90
Purchase #6	$247.50	3.261%	$255.571	$255.57	$255.55	$255.60
Purchase #7	$35.31	12.786%	$39.8247	$39.82	$39.80	$39.80
7 purchase totals =	$1,203.61		$1,284.7572	$1,284.75	$1,284.70	$1,284.70