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	$78.72	5.611%	$83.137	$83.14	$83.15	$83.10
Purchase #2	$146.36	12.578%	$164.7692	$164.77	$164.75	$164.80
Purchase #3	$10.53	5.869%	$11.148	$11.15	$11.15	$11.10
Purchase #4	$55.81	6.278%	$59.3138	$59.31	$59.30	$59.30
Purchase #5	$150.95	10.301%	$166.4994	$166.50	$166.50	$166.50
Purchase #6	$167.73	13.254%	$189.9609	$189.96	$189.95	$190.00
Purchase #7	$101.37	11.464%	$112.9911	$112.99	$113.00	$113.00
7 purchase totals =	$711.47		$787.8194	$787.82	$787.80	$787.80