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	$91.46	8.576%	$99.3036	$99.30	$99.30	$99.30
Purchase #2	$49.54	5.355%	$52.1929	$52.19	$52.20	$52.20
Purchase #3	$100.63	11.660%	$112.3635	$112.36	$112.35	$112.40
Purchase #4	$215.51	13.196%	$243.9487	$243.95	$243.95	$243.90
Purchase #5	$234.94	8.252%	$254.3272	$254.33	$254.35	$254.30
Purchase #6	$212.32	13.266%	$240.4864	$240.49	$240.50	$240.50
Purchase #7	$35.40	7.185%	$37.9435	$37.94	$37.95	$37.90
7 purchase totals =	$939.80		$1,040.5658	$1,040.56	$1,040.60	$1,040.50