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	$179.35	5.223%	$188.7175	$188.72	$188.70	$188.70
Purchase #2	$61.47	10.585%	$67.9766	$67.98	$68.00	$68.00
Purchase #3	$148.88	12.443%	$167.4051	$167.41	$167.40	$167.40
Purchase #4	$133.57	12.700%	$150.5334	$150.53	$150.55	$150.50
Purchase #5	$93.66	9.474%	$102.5333	$102.53	$102.55	$102.50
Purchase #6	$151.58	13.275%	$171.7022	$171.70	$171.70	$171.70
Purchase #7	$136.96	13.825%	$155.8947	$155.89	$155.90	$155.90
7 purchase totals =	$905.47		$1,004.7628	$1,004.76	$1,004.80	$1,004.70