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	$52.93	12.558%	$59.5769	$59.58	$59.60	$59.60
Purchase #2	$96.32	13.284%	$109.1151	$109.12	$109.10	$109.10
Purchase #3	$166.89	8.129%	$180.4565	$180.46	$180.45	$180.50
Purchase #4	$240.98	9.117%	$262.9501	$262.95	$262.95	$263.00
Purchase #5	$119.66	12.167%	$134.219	$134.22	$134.20	$134.20
Purchase #6	$192.76	9.401%	$210.8814	$210.88	$210.90	$210.90
Purchase #7	$175.80	9.166%	$191.9138	$191.91	$191.90	$191.90
7 purchase totals =	$1,045.34		$1,149.1128	$1,149.12	$1,149.10	$1,149.20