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	$183.29	8.168%	$198.2611	$198.26	$198.25	$198.30
Purchase #2	$10.76	12.433%	$12.0978	$12.10	$12.10	$12.10
Purchase #3	$112.57	9.559%	$123.3306	$123.33	$123.35	$123.30
Purchase #4	$242.56	8.231%	$262.5251	$262.53	$262.55	$262.50
Purchase #5	$199.99	11.115%	$222.2189	$222.22	$222.20	$222.20
Purchase #6	$39.56	3.701%	$41.0241	$41.02	$41.00	$41.00
Purchase #7	$72.48	11.122%	$80.5412	$80.54	$80.55	$80.50
7 purchase totals =	$861.21		$939.9988	$940.00	$940.00	$939.90