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	$42.27	6.795%	$45.1422	$45.14	$45.15	$45.10
Purchase #2	$201.59	13.386%	$228.5748	$228.57	$228.55	$228.60
Purchase #3	$36.58	4.250%	$38.1347	$38.13	$38.15	$38.10
Purchase #4	$124.61	6.480%	$132.6847	$132.68	$132.70	$132.70
Purchase #5	$228.89	6.330%	$243.3787	$243.38	$243.40	$243.40
Purchase #6	$148.95	4.271%	$155.3117	$155.31	$155.30	$155.30
Purchase #7	$250.94	9.146%	$273.891	$273.89	$273.90	$273.90
7 purchase totals =	$1,033.83		$1,117.1178	$1,117.10	$1,117.15	$1,117.10