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	$68.30	10.200%	$75.2666	$75.27	$75.25	$75.30
Purchase #2	$46.44	8.822%	$50.5369	$50.54	$50.55	$50.50
Purchase #3	$147.34	13.664%	$167.4725	$167.47	$167.45	$167.50
Purchase #4	$247.98	4.551%	$259.2656	$259.27	$259.25	$259.30
Purchase #5	$185.50	6.818%	$198.1474	$198.15	$198.15	$198.10
Purchase #6	$210.98	5.851%	$223.3244	$223.32	$223.30	$223.30
Purchase #7	$86.58	6.507%	$92.2138	$92.21	$92.20	$92.20
7 purchase totals =	$993.12		$1,066.2272	$1,066.23	$1,066.15	$1,066.20