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	$24.80	10.135%	$27.3135	$27.31	$27.30	$27.30
Purchase #2	$223.85	7.821%	$241.3573	$241.36	$241.35	$241.40
Purchase #3	$247.42	10.729%	$273.9657	$273.97	$273.95	$274.00
Purchase #4	$99.39	10.559%	$109.8846	$109.88	$109.90	$109.90
Purchase #5	$129.25	10.502%	$142.8238	$142.82	$142.80	$142.80
Purchase #6	$185.44	9.411%	$202.8918	$202.89	$202.90	$202.90
Purchase #7	$89.26	11.872%	$99.8569	$99.86	$99.85	$99.90
7 purchase totals =	$999.41		$1,098.0936	$1,098.09	$1,098.05	$1,098.20