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	$35.94	13.863%	$40.9224	$40.92	$40.90	$40.90
Purchase #2	$174.46	12.513%	$196.2902	$196.29	$196.30	$196.30
Purchase #3	$211.31	7.751%	$227.6886	$227.69	$227.70	$227.70
Purchase #4	$45.42	3.717%	$47.1083	$47.11	$47.10	$47.10
Purchase #5	$39.38	10.371%	$43.4641	$43.46	$43.45	$43.50
Purchase #6	$168.30	10.453%	$185.8924	$185.89	$185.90	$185.90
Purchase #7	$80.88	3.500%	$83.7108	$83.71	$83.70	$83.70
7 purchase totals =	$755.69		$825.0768	$825.07	$825.05	$825.10