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	$70.32	11.766%	$78.5939	$78.59	$78.60	$78.60
Purchase #2	$104.84	9.461%	$114.7589	$114.76	$114.75	$114.80
Purchase #3	$87.87	8.833%	$95.6316	$95.63	$95.65	$95.60
Purchase #4	$7.46	3.866%	$7.7484	$7.75	$7.75	$7.70
Purchase #5	$32.33	3.146%	$33.3471	$33.35	$33.35	$33.30
Purchase #6	$83.76	6.212%	$88.9632	$88.96	$88.95	$89.00
Purchase #7	$133.91	12.438%	$150.5657	$150.57	$150.55	$150.60
7 purchase totals =	$520.49		$569.6088	$569.61	$569.60	$569.60