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	$67.99	5.755%	$71.9028	$71.90	$71.90	$71.90
Purchase #2	$245.90	7.490%	$264.3179	$264.32	$264.30	$264.30
Purchase #3	$42.63	4.220%	$44.429	$44.43	$44.45	$44.40
Purchase #4	$202.42	6.416%	$215.4073	$215.41	$215.40	$215.40
Purchase #5	$122.50	7.805%	$132.0611	$132.06	$132.05	$132.10
Purchase #6	$38.86	8.466%	$42.1499	$42.15	$42.15	$42.10
Purchase #7	$64.87	9.534%	$71.0547	$71.05	$71.05	$71.10
7 purchase totals =	$785.17		$841.3227	$841.32	$841.30	$841.30