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	$20.45	11.303%	$22.7615	$22.76	$22.75	$22.80
Purchase #2	$191.70	9.616%	$210.1339	$210.13	$210.15	$210.10
Purchase #3	$122.98	6.749%	$131.2799	$131.28	$131.30	$131.30
Purchase #4	$76.91	8.715%	$83.6127	$83.61	$83.60	$83.60
Purchase #5	$64.93	11.380%	$72.319	$72.32	$72.30	$72.30
Purchase #6	$189.92	12.435%	$213.5366	$213.54	$213.55	$213.50
Purchase #7	$131.32	9.597%	$143.9228	$143.92	$143.90	$143.90
7 purchase totals =	$798.21		$877.5664	$877.56	$877.55	$877.50