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	$126.85	11.562%	$141.5164	$141.52	$141.50	$141.50
Purchase #2	$249.46	8.372%	$270.3448	$270.34	$270.35	$270.30
Purchase #3	$91.31	9.563%	$100.042	$100.04	$100.05	$100.00
Purchase #4	$37.56	12.444%	$42.234	$42.23	$42.25	$42.20
Purchase #5	$179.96	8.366%	$195.0155	$195.02	$195.00	$195.00
Purchase #6	$13.40	9.833%	$14.7176	$14.72	$14.70	$14.70
Purchase #7	$38.89	6.279%	$41.3319	$41.33	$41.35	$41.30
7 purchase totals =	$737.43		$805.2022	$805.20	$805.20	$805.00