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	$184.67	3.700%	$191.5028	$191.50	$191.50	$191.50
Purchase #2	$194.25	9.111%	$211.9481	$211.95	$211.95	$211.90
Purchase #3	$151.51	8.543%	$164.4535	$164.45	$164.45	$164.50
Purchase #4	$58.72	8.743%	$63.8539	$63.85	$63.85	$63.90
Purchase #5	$32.65	11.290%	$36.3362	$36.34	$36.35	$36.30
Purchase #6	$84.82	6.168%	$90.0517	$90.05	$90.05	$90.10
Purchase #7	$86.46	3.383%	$89.3849	$89.38	$89.40	$89.40
7 purchase totals =	$793.08		$847.5311	$847.52	$847.55	$847.60