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	$250.66	9.118%	$273.5152	$273.52	$273.50	$273.50
Purchase #2	$179.28	8.292%	$194.1459	$194.15	$194.15	$194.10
Purchase #3	$139.51	9.347%	$152.55	$152.55	$152.55	$152.60
Purchase #4	$180.76	8.740%	$196.5584	$196.56	$196.55	$196.60
Purchase #5	$51.58	4.508%	$53.9052	$53.91	$53.90	$53.90
Purchase #6	$201.40	8.475%	$218.4687	$218.47	$218.45	$218.50
Purchase #7	$209.66	12.832%	$236.5636	$236.56	$236.55	$236.60
7 purchase totals =	$1,212.85		$1,325.7070	$1,325.72	$1,325.65	$1,325.80