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	$170.90	5.788%	$180.7917	$180.79	$180.80	$180.80
Purchase #2	$178.43	8.148%	$192.9685	$192.97	$192.95	$193.00
Purchase #3	$54.93	8.204%	$59.4365	$59.44	$59.45	$59.40
Purchase #4	$139.55	3.768%	$144.8082	$144.81	$144.80	$144.80
Purchase #5	$66.33	8.398%	$71.9004	$71.90	$71.90	$71.90
Purchase #6	$113.46	13.308%	$128.5593	$128.56	$128.55	$128.60
Purchase #7	$122.73	13.106%	$138.815	$138.82	$138.80	$138.80
7 purchase totals =	$846.33		$917.2796	$917.29	$917.25	$917.30