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	$181.40	12.179%	$203.4927	$203.49	$203.50	$203.50
Purchase #2	$61.89	8.693%	$67.2701	$67.27	$67.25	$67.30
Purchase #3	$63.47	5.586%	$67.0154	$67.02	$67.00	$67.00
Purchase #4	$85.57	4.627%	$89.5293	$89.53	$89.55	$89.50
Purchase #5	$203.88	11.645%	$227.6218	$227.62	$227.60	$227.60
Purchase #6	$249.60	7.729%	$268.8916	$268.89	$268.90	$268.90
Purchase #7	$192.31	7.137%	$206.0352	$206.04	$206.05	$206.00
7 purchase totals =	$1,038.12		$1,129.8561	$1,129.86	$1,129.85	$1,129.80