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	$126.96	7.761%	$136.8134	$136.81	$136.80	$136.80
Purchase #2	$112.77	5.821%	$119.3343	$119.33	$119.35	$119.30
Purchase #3	$208.28	9.149%	$227.3355	$227.34	$227.35	$227.30
Purchase #4	$186.88	12.640%	$210.5016	$210.50	$210.50	$210.50
Purchase #5	$143.53	6.231%	$152.4734	$152.47	$152.45	$152.50
Purchase #6	$125.90	10.583%	$139.224	$139.22	$139.20	$139.20
Purchase #7	$33.98	3.672%	$35.2277	$35.23	$35.25	$35.20
7 purchase totals =	$938.30		$1,020.9099	$1,020.90	$1,020.90	$1,020.80