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	$36.53	11.533%	$40.743	$40.74	$40.75	$40.70
Purchase #2	$159.76	7.417%	$171.6094	$171.61	$171.60	$171.60
Purchase #3	$87.69	8.460%	$95.1086	$95.11	$95.10	$95.10
Purchase #4	$220.39	9.116%	$240.4808	$240.48	$240.50	$240.50
Purchase #5	$42.90	5.725%	$45.356	$45.36	$45.35	$45.40
Purchase #6	$80.34	7.609%	$86.4531	$86.45	$86.45	$86.50
Purchase #7	$148.46	12.574%	$167.1274	$167.13	$167.15	$167.10
7 purchase totals =	$776.07		$846.8783	$846.88	$846.90	$846.90