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	$97.31	3.710%	$100.9202	$100.92	$100.90	$100.90
Purchase #2	$155.71	10.423%	$171.9397	$171.94	$171.95	$171.90
Purchase #3	$35.95	7.288%	$38.57	$38.57	$38.55	$38.60
Purchase #4	$81.41	13.736%	$92.5925	$92.59	$92.60	$92.60
Purchase #5	$97.89	6.417%	$104.1716	$104.17	$104.15	$104.20
Purchase #6	$166.25	13.625%	$188.9016	$188.90	$188.90	$188.90
Purchase #7	$107.48	4.220%	$112.0157	$112.02	$112.00	$112.00
7 purchase totals =	$742.00		$809.1113	$809.11	$809.05	$809.10