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	$133.71	10.744%	$148.0758	$148.08	$148.10	$148.10
Purchase #2	$154.38	6.244%	$164.0195	$164.02	$164.00	$164.00
Purchase #3	$80.82	12.571%	$90.9799	$90.98	$91.00	$91.00
Purchase #4	$85.55	13.271%	$96.9033	$96.90	$96.90	$96.90
Purchase #5	$227.93	6.740%	$243.2925	$243.29	$243.30	$243.30
Purchase #6	$82.98	9.328%	$90.7204	$90.72	$90.70	$90.70
Purchase #7	$161.45	6.328%	$171.6666	$171.67	$171.65	$171.70
7 purchase totals =	$926.82		$1,005.6580	$1,005.66	$1,005.65	$1,005.70