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	$38.41	13.517%	$43.6019	$43.60	$43.60	$43.60
Purchase #2	$86.90	8.726%	$94.4829	$94.48	$94.50	$94.50
Purchase #3	$45.62	11.276%	$50.7641	$50.76	$50.75	$50.80
Purchase #4	$201.30	8.737%	$218.8876	$218.89	$218.90	$218.90
Purchase #5	$204.36	11.659%	$228.1863	$228.19	$228.20	$228.20
Purchase #6	$146.61	8.120%	$158.5147	$158.51	$158.50	$158.50
Purchase #7	$208.34	13.189%	$235.818	$235.82	$235.80	$235.80
7 purchase totals =	$931.54		$1,030.2555	$1,030.25	$1,030.25	$1,030.30