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	$232.45	12.668%	$261.8968	$261.90	$261.90	$261.90
Purchase #2	$141.53	7.588%	$152.2693	$152.27	$152.25	$152.30
Purchase #3	$50.72	13.177%	$57.4034	$57.40	$57.40	$57.40
Purchase #4	$158.53	4.705%	$165.9888	$165.99	$166.00	$166.00
Purchase #5	$61.90	6.273%	$65.783	$65.78	$65.80	$65.80
Purchase #6	$241.57	11.552%	$269.4762	$269.48	$269.50	$269.50
Purchase #7	$63.26	7.192%	$67.8097	$67.81	$67.80	$67.80
7 purchase totals =	$949.96		$1,040.6272	$1,040.63	$1,040.65	$1,040.70