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	$243.59	4.612%	$254.8244	$254.82	$254.80	$254.80
Purchase #2	$181.49	5.555%	$191.5718	$191.57	$191.55	$191.60
Purchase #3	$75.63	3.785%	$78.4926	$78.49	$78.50	$78.50
Purchase #4	$145.78	4.433%	$152.2424	$152.24	$152.25	$152.20
Purchase #5	$57.72	8.302%	$62.5119	$62.51	$62.50	$62.50
Purchase #6	$87.98	13.506%	$99.8626	$99.86	$99.85	$99.90
Purchase #7	$79.96	8.551%	$86.7974	$86.80	$86.80	$86.80
7 purchase totals =	$872.15		$926.3031	$926.29	$926.25	$926.30