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	$7.32	5.516%	$7.7238	$7.72	$7.70	$7.70
Purchase #2	$166.43	11.680%	$185.869	$185.87	$185.85	$185.90
Purchase #3	$183.77	6.790%	$196.248	$196.25	$196.25	$196.20
Purchase #4	$178.85	9.529%	$195.8926	$195.89	$195.90	$195.90
Purchase #5	$234.86	13.737%	$267.1227	$267.12	$267.10	$267.10
Purchase #6	$152.64	9.865%	$167.6979	$167.70	$167.70	$167.70
Purchase #7	$194.58	11.700%	$217.3459	$217.35	$217.35	$217.30
7 purchase totals =	$1,118.45		$1,237.8999	$1,237.90	$1,237.85	$1,237.80