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	$76.67	9.133%	$83.6723	$83.67	$83.65	$83.70
Purchase #2	$39.98	9.848%	$43.9172	$43.92	$43.90	$43.90
Purchase #3	$171.33	10.288%	$188.9564	$188.96	$188.95	$189.00
Purchase #4	$149.82	12.294%	$168.2389	$168.24	$168.25	$168.20
Purchase #5	$236.46	7.472%	$254.1283	$254.13	$254.15	$254.10
Purchase #6	$197.82	12.184%	$221.9224	$221.92	$221.90	$221.90
Purchase #7	$42.70	6.602%	$45.5191	$45.52	$45.50	$45.50
7 purchase totals =	$914.78		$1,006.3546	$1,006.36	$1,006.30	$1,006.30