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	$94.68	3.664%	$98.1491	$98.15	$98.15	$98.10
Purchase #2	$117.73	11.229%	$130.9499	$130.95	$130.95	$130.90
Purchase #3	$176.32	13.562%	$200.2325	$200.23	$200.25	$200.20
Purchase #4	$229.72	4.831%	$240.8178	$240.82	$240.80	$240.80
Purchase #5	$26.40	13.290%	$29.9086	$29.91	$29.90	$29.90
Purchase #6	$177.72	6.223%	$188.7795	$188.78	$188.80	$188.80
Purchase #7	$156.71	13.553%	$177.9489	$177.95	$177.95	$177.90
7 purchase totals =	$979.28		$1,066.7863	$1,066.79	$1,066.80	$1,066.60