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	$52.42	5.526%	$55.3167	$55.32	$55.30	$55.30
Purchase #2	$195.53	10.271%	$215.6129	$215.61	$215.60	$215.60
Purchase #3	$182.56	7.650%	$196.5258	$196.53	$196.55	$196.50
Purchase #4	$146.72	8.752%	$159.5609	$159.56	$159.55	$159.60
Purchase #5	$234.87	6.531%	$250.2094	$250.21	$250.20	$250.20
Purchase #6	$111.85	7.552%	$120.2969	$120.30	$120.30	$120.30
Purchase #7	$140.53	13.365%	$159.3118	$159.31	$159.30	$159.30
7 purchase totals =	$1,064.48		$1,156.8344	$1,156.84	$1,156.80	$1,156.80