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	$105.54	7.165%	$113.1019	$113.10	$113.10	$113.10
Purchase #2	$90.61	9.725%	$99.4218	$99.42	$99.40	$99.40
Purchase #3	$65.61	9.203%	$71.6481	$71.65	$71.65	$71.60
Purchase #4	$168.28	9.462%	$184.2027	$184.20	$184.20	$184.20
Purchase #5	$231.63	7.404%	$248.7799	$248.78	$248.80	$248.80
Purchase #6	$145.67	11.662%	$162.658	$162.66	$162.65	$162.70
Purchase #7	$196.43	3.797%	$203.8884	$203.89	$203.90	$203.90
7 purchase totals =	$1,003.77		$1,083.7008	$1,083.70	$1,083.70	$1,083.70