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	$128.61	8.515%	$139.5611	$139.56	$139.55	$139.60
Purchase #2	$41.52	8.773%	$45.1625	$45.16	$45.15	$45.20
Purchase #3	$140.35	7.610%	$151.0306	$151.03	$151.05	$151.00
Purchase #4	$213.67	3.334%	$220.7938	$220.79	$220.80	$220.80
Purchase #5	$83.63	6.774%	$89.2951	$89.30	$89.30	$89.30
Purchase #6	$221.95	10.279%	$244.7642	$244.76	$244.75	$244.80
Purchase #7	$178.59	7.872%	$192.6486	$192.65	$192.65	$192.60
7 purchase totals =	$1,008.32		$1,083.2559	$1,083.25	$1,083.25	$1,083.30