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	$163.39	4.848%	$171.3111	$171.31	$171.30	$171.30
Purchase #2	$221.92	8.532%	$240.8542	$240.85	$240.85	$240.90
Purchase #3	$247.96	8.297%	$268.5332	$268.53	$268.55	$268.50
Purchase #4	$32.61	10.735%	$36.1107	$36.11	$36.10	$36.10
Purchase #5	$131.88	11.578%	$147.1491	$147.15	$147.15	$147.10
Purchase #6	$222.70	10.515%	$246.1169	$246.12	$246.10	$246.10
Purchase #7	$71.61	10.220%	$78.9285	$78.93	$78.95	$78.90
7 purchase totals =	$1,092.07		$1,189.0037	$1,189.00	$1,189.00	$1,188.90