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	$7.78	7.870%	$8.3923	$8.39	$8.40	$8.40
Purchase #2	$53.64	5.850%	$56.7779	$56.78	$56.80	$56.80
Purchase #3	$68.53	3.642%	$71.0259	$71.03	$71.05	$71.00
Purchase #4	$218.73	4.288%	$228.1091	$228.11	$228.10	$228.10
Purchase #5	$134.57	3.646%	$139.4764	$139.48	$139.50	$139.50
Purchase #6	$212.91	12.792%	$240.1454	$240.15	$240.15	$240.10
Purchase #7	$52.65	12.729%	$59.3518	$59.35	$59.35	$59.40
7 purchase totals =	$748.81		$803.2788	$803.29	$803.35	$803.30