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	$42.96	5.603%	$45.367	$45.37	$45.35	$45.40
Purchase #2	$243.75	12.173%	$273.4217	$273.42	$273.40	$273.40
Purchase #3	$61.81	5.866%	$65.4358	$65.44	$65.45	$65.40
Purchase #4	$131.89	6.243%	$140.1239	$140.12	$140.10	$140.10
Purchase #5	$6.80	3.414%	$7.0322	$7.03	$7.05	$7.00
Purchase #6	$155.83	11.780%	$174.1868	$174.19	$174.20	$174.20
Purchase #7	$115.50	10.248%	$127.3364	$127.34	$127.35	$127.30
7 purchase totals =	$758.54		$832.9038	$832.91	$832.90	$832.80