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	$68.73	3.756%	$71.3115	$71.31	$71.30	$71.30
Purchase #2	$36.93	9.714%	$40.5174	$40.52	$40.50	$40.50
Purchase #3	$221.88	7.200%	$237.8554	$237.86	$237.85	$237.90
Purchase #4	$136.66	6.254%	$145.2067	$145.21	$145.20	$145.20
Purchase #5	$228.27	6.206%	$242.4364	$242.44	$242.45	$242.40
Purchase #6	$42.43	7.647%	$45.6746	$45.67	$45.65	$45.70
Purchase #7	$201.92	9.172%	$220.4401	$220.44	$220.45	$220.40
7 purchase totals =	$936.82		$1,003.4421	$1,003.45	$1,003.40	$1,003.40