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	$40.45	6.295%	$42.9963	$43.00	$43.00	$43.00
Purchase #2	$131.61	12.192%	$147.6559	$147.66	$147.65	$147.70
Purchase #3	$133.71	9.533%	$146.4566	$146.46	$146.45	$146.50
Purchase #4	$77.80	8.609%	$84.4978	$84.50	$84.50	$84.50
Purchase #5	$143.69	11.125%	$159.6755	$159.68	$159.70	$159.70
Purchase #6	$31.55	13.761%	$35.8916	$35.89	$35.90	$35.90
Purchase #7	$77.48	6.649%	$82.6316	$82.63	$82.65	$82.60
7 purchase totals =	$636.29		$699.8053	$699.82	$699.85	$699.90