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	$91.45	8.623%	$99.3357	$99.34	$99.35	$99.30
Purchase #2	$244.43	3.853%	$253.8479	$253.85	$253.85	$253.80
Purchase #3	$135.99	3.715%	$141.042	$141.04	$141.05	$141.00
Purchase #4	$220.55	11.311%	$245.4964	$245.50	$245.50	$245.50
Purchase #5	$89.46	7.224%	$95.9226	$95.92	$95.90	$95.90
Purchase #6	$124.85	12.465%	$140.4126	$140.41	$140.40	$140.40
Purchase #7	$29.39	7.538%	$31.6054	$31.61	$31.60	$31.60
7 purchase totals =	$936.12		$1,007.6626	$1,007.67	$1,007.65	$1,007.50