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	$77.52	5.835%	$82.0433	$82.04	$82.05	$82.00
Purchase #2	$246.54	7.700%	$265.5236	$265.52	$265.50	$265.50
Purchase #3	$103.92	7.629%	$111.8481	$111.85	$111.85	$111.80
Purchase #4	$170.69	4.855%	$178.977	$178.98	$179.00	$179.00
Purchase #5	$211.33	6.712%	$225.5145	$225.51	$225.50	$225.50
Purchase #6	$72.76	7.377%	$78.1275	$78.13	$78.15	$78.10
Purchase #7	$36.61	3.480%	$37.884	$37.88	$37.90	$37.90
7 purchase totals =	$919.37		$979.9180	$979.91	$979.95	$979.80