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	$39.61	5.807%	$41.9102	$41.91	$41.90	$41.90
Purchase #2	$186.25	7.843%	$200.8576	$200.86	$200.85	$200.90
Purchase #3	$96.74	9.422%	$105.8548	$105.85	$105.85	$105.90
Purchase #4	$160.29	11.820%	$179.2363	$179.24	$179.25	$179.20
Purchase #5	$123.39	12.361%	$138.6422	$138.64	$138.65	$138.60
Purchase #6	$182.65	11.372%	$203.421	$203.42	$203.40	$203.40
Purchase #7	$228.36	12.285%	$256.414	$256.41	$256.40	$256.40
7 purchase totals =	$1,017.29		$1,126.3361	$1,126.33	$1,126.30	$1,126.30