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	$77.69	3.129%	$80.1209	$80.12	$80.10	$80.10
Purchase #2	$136.89	7.626%	$147.3292	$147.33	$147.35	$147.30
Purchase #3	$245.43	9.788%	$269.4527	$269.45	$269.45	$269.50
Purchase #4	$61.69	6.472%	$65.6826	$65.68	$65.70	$65.70
Purchase #5	$113.44	8.440%	$123.0143	$123.01	$123.00	$123.00
Purchase #6	$44.44	6.825%	$47.473	$47.47	$47.45	$47.50
Purchase #7	$64.25	11.116%	$71.392	$71.39	$71.40	$71.40
7 purchase totals =	$743.83		$804.4647	$804.45	$804.45	$804.50