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	$57.26	4.473%	$59.8212	$59.82	$59.80	$59.80
Purchase #2	$189.66	4.609%	$198.4014	$198.40	$198.40	$198.40
Purchase #3	$61.53	9.687%	$67.4904	$67.49	$67.50	$67.50
Purchase #4	$42.25	12.645%	$47.5925	$47.59	$47.60	$47.60
Purchase #5	$180.33	7.561%	$193.9648	$193.96	$193.95	$194.00
Purchase #6	$240.76	4.183%	$250.831	$250.83	$250.85	$250.80
Purchase #7	$84.95	7.766%	$91.5472	$91.55	$91.55	$91.50
7 purchase totals =	$856.74		$909.6485	$909.64	$909.65	$909.60