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	$121.46	6.759%	$129.6695	$129.67	$129.65	$129.70
Purchase #2	$78.99	13.707%	$89.8172	$89.82	$89.80	$89.80
Purchase #3	$43.43	4.432%	$45.3548	$45.35	$45.35	$45.40
Purchase #4	$73.45	5.412%	$77.4251	$77.43	$77.45	$77.40
Purchase #5	$207.46	7.178%	$222.3515	$222.35	$222.35	$222.40
Purchase #6	$134.94	11.424%	$150.3555	$150.36	$150.35	$150.40
Purchase #7	$171.68	3.868%	$178.3206	$178.32	$178.30	$178.30
7 purchase totals =	$831.41		$893.2942	$893.30	$893.25	$893.40