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	$170.38	12.591%	$191.8325	$191.83	$191.85	$191.80
Purchase #2	$141.72	3.352%	$146.4705	$146.47	$146.45	$146.50
Purchase #3	$168.97	6.385%	$179.7587	$179.76	$179.75	$179.80
Purchase #4	$246.60	11.221%	$274.271	$274.27	$274.25	$274.30
Purchase #5	$88.84	6.155%	$94.3081	$94.31	$94.30	$94.30
Purchase #6	$149.71	9.555%	$164.0148	$164.01	$164.00	$164.00
Purchase #7	$226.27	5.610%	$238.9637	$238.96	$238.95	$239.00
7 purchase totals =	$1,192.49		$1,289.6193	$1,289.61	$1,289.55	$1,289.70