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	$170.63	12.147%	$191.3564	$191.36	$191.35	$191.40
Purchase #2	$23.83	6.410%	$25.3575	$25.36	$25.35	$25.40
Purchase #3	$91.35	9.164%	$99.7213	$99.72	$99.70	$99.70
Purchase #4	$187.89	4.393%	$196.144	$196.14	$196.15	$196.10
Purchase #5	$104.52	8.518%	$113.423	$113.42	$113.40	$113.40
Purchase #6	$92.38	5.242%	$97.2226	$97.22	$97.20	$97.20
Purchase #7	$219.31	11.120%	$243.6973	$243.70	$243.70	$243.70
7 purchase totals =	$889.91		$966.9221	$966.92	$966.85	$966.90