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	$199.91	3.744%	$207.3946	$207.39	$207.40	$207.40
Purchase #2	$92.53	11.130%	$102.8286	$102.83	$102.85	$102.80
Purchase #3	$53.33	11.614%	$59.5237	$59.52	$59.50	$59.50
Purchase #4	$58.96	6.547%	$62.8201	$62.82	$62.80	$62.80
Purchase #5	$206.50	8.159%	$223.3483	$223.35	$223.35	$223.30
Purchase #6	$244.33	9.828%	$268.3428	$268.34	$268.35	$268.30
Purchase #7	$129.85	9.336%	$141.9728	$141.97	$141.95	$142.00
7 purchase totals =	$985.41		$1,066.2309	$1,066.22	$1,066.20	$1,066.10