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	$81.94	8.869%	$89.2073	$89.21	$89.20	$89.20
Purchase #2	$89.52	10.794%	$99.1828	$99.18	$99.20	$99.20
Purchase #3	$41.38	5.809%	$43.7838	$43.78	$43.80	$43.80
Purchase #4	$84.78	11.564%	$94.584	$94.58	$94.60	$94.60
Purchase #5	$130.53	9.300%	$142.6693	$142.67	$142.65	$142.70
Purchase #6	$124.36	12.709%	$140.1649	$140.16	$140.15	$140.20
Purchase #7	$200.72	12.702%	$226.2155	$226.22	$226.20	$226.20
7 purchase totals =	$753.23		$835.8076	$835.80	$835.80	$835.90