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	$6.28	4.262%	$6.5477	$6.55	$6.55	$6.50
Purchase #2	$205.37	3.784%	$213.1412	$213.14	$213.15	$213.10
Purchase #3	$159.63	6.413%	$169.8671	$169.87	$169.85	$169.90
Purchase #4	$223.94	11.264%	$249.1646	$249.16	$249.15	$249.20
Purchase #5	$137.48	11.246%	$152.941	$152.94	$152.95	$152.90
Purchase #6	$209.36	9.807%	$229.8919	$229.89	$229.90	$229.90
Purchase #7	$65.43	9.679%	$71.763	$71.76	$71.75	$71.80
7 purchase totals =	$1,007.49		$1,093.3165	$1,093.31	$1,093.30	$1,093.30