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	$205.47	11.647%	$229.4011	$229.40	$229.40	$229.40
Purchase #2	$245.28	11.400%	$273.2419	$273.24	$273.25	$273.20
Purchase #3	$135.84	5.175%	$142.8697	$142.87	$142.85	$142.90
Purchase #4	$121.82	7.579%	$131.0527	$131.05	$131.05	$131.10
Purchase #5	$79.50	13.696%	$90.3883	$90.39	$90.40	$90.40
Purchase #6	$61.75	13.206%	$69.9047	$69.90	$69.90	$69.90
Purchase #7	$53.69	10.872%	$59.5272	$59.53	$59.55	$59.50
7 purchase totals =	$903.35		$996.3856	$996.38	$996.40	$996.40