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	$88.39	12.411%	$99.3601	$99.36	$99.35	$99.40
Purchase #2	$243.51	10.308%	$268.611	$268.61	$268.60	$268.60
Purchase #3	$156.46	6.216%	$166.1856	$166.19	$166.20	$166.20
Purchase #4	$109.34	13.204%	$123.7773	$123.78	$123.80	$123.80
Purchase #5	$142.91	12.261%	$160.4322	$160.43	$160.45	$160.40
Purchase #6	$116.62	10.561%	$128.9362	$128.94	$128.95	$128.90
Purchase #7	$236.96	10.500%	$261.8408	$261.84	$261.85	$261.80
7 purchase totals =	$1,094.19		$1,209.1432	$1,209.15	$1,209.20	$1,209.10