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	$250.50	10.708%	$277.3235	$277.32	$277.30	$277.30
Purchase #2	$113.57	10.276%	$125.2405	$125.24	$125.25	$125.20
Purchase #3	$174.69	12.285%	$196.1507	$196.15	$196.15	$196.20
Purchase #4	$85.87	11.414%	$95.6712	$95.67	$95.65	$95.70
Purchase #5	$84.65	5.272%	$89.1127	$89.11	$89.10	$89.10
Purchase #6	$234.98	9.589%	$257.5122	$257.51	$257.50	$257.50
Purchase #7	$68.83	5.105%	$72.3438	$72.34	$72.35	$72.30
7 purchase totals =	$1,013.09		$1,113.3546	$1,113.34	$1,113.30	$1,113.30