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	$243.58	12.188%	$273.2675	$273.27	$273.25	$273.30
Purchase #2	$219.57	7.874%	$236.8589	$236.86	$236.85	$236.90
Purchase #3	$48.39	12.715%	$54.5428	$54.54	$54.55	$54.50
Purchase #4	$97.84	7.814%	$105.4852	$105.49	$105.50	$105.50
Purchase #5	$190.42	3.332%	$196.7648	$196.76	$196.75	$196.80
Purchase #6	$54.25	9.824%	$59.5795	$59.58	$59.60	$59.60
Purchase #7	$151.42	9.753%	$166.188	$166.19	$166.20	$166.20
7 purchase totals =	$1,005.47		$1,092.6867	$1,092.69	$1,092.70	$1,092.80