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	$37.74	7.404%	$40.5343	$40.53	$40.55	$40.50
Purchase #2	$120.58	8.136%	$130.3904	$130.39	$130.40	$130.40
Purchase #3	$115.78	3.244%	$119.5359	$119.54	$119.55	$119.50
Purchase #4	$132.32	9.617%	$145.0452	$145.05	$145.05	$145.00
Purchase #5	$84.34	5.779%	$89.214	$89.21	$89.20	$89.20
Purchase #6	$168.65	7.126%	$180.668	$180.67	$180.65	$180.70
Purchase #7	$86.69	9.765%	$95.1553	$95.16	$95.15	$95.20
7 purchase totals =	$746.10		$800.5431	$800.55	$800.55	$800.50