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	$93.79	12.500%	$105.5138	$105.51	$105.50	$105.50
Purchase #2	$86.91	5.235%	$91.4597	$91.46	$91.45	$91.50
Purchase #3	$86.69	7.164%	$92.9005	$92.90	$92.90	$92.90
Purchase #4	$168.34	7.165%	$180.4016	$180.40	$180.40	$180.40
Purchase #5	$110.95	7.134%	$118.8652	$118.87	$118.85	$118.90
Purchase #6	$161.69	5.119%	$169.9669	$169.97	$169.95	$170.00
Purchase #7	$225.74	3.360%	$233.3249	$233.32	$233.30	$233.30
7 purchase totals =	$934.11		$992.4326	$992.43	$992.35	$992.50