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	$206.48	5.713%	$218.2762	$218.28	$218.30	$218.30
Purchase #2	$71.70	13.427%	$81.3272	$81.33	$81.35	$81.30
Purchase #3	$125.65	12.297%	$141.1012	$141.10	$141.10	$141.10
Purchase #4	$43.41	6.650%	$46.2968	$46.30	$46.30	$46.30
Purchase #5	$250.59	7.300%	$268.8831	$268.88	$268.90	$268.90
Purchase #6	$196.38	11.718%	$219.3918	$219.39	$219.40	$219.40
Purchase #7	$149.67	11.693%	$167.1709	$167.17	$167.15	$167.20
7 purchase totals =	$1,043.88		$1,142.4472	$1,142.45	$1,142.50	$1,142.50