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	$178.70	5.789%	$189.0449	$189.04	$189.05	$189.00
Purchase #2	$160.80	7.659%	$173.1157	$173.12	$173.10	$173.10
Purchase #3	$118.76	10.457%	$131.1787	$131.18	$131.20	$131.20
Purchase #4	$152.32	7.809%	$164.2147	$164.21	$164.20	$164.20
Purchase #5	$99.25	10.410%	$109.5819	$109.58	$109.60	$109.60
Purchase #6	$189.30	11.538%	$211.1414	$211.14	$211.15	$211.10
Purchase #7	$151.81	10.735%	$168.1068	$168.11	$168.10	$168.10
7 purchase totals =	$1,050.94		$1,146.3841	$1,146.38	$1,146.40	$1,146.30