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	$172.48	3.330%	$178.2236	$178.22	$178.20	$178.20
Purchase #2	$169.71	11.850%	$189.8206	$189.82	$189.80	$189.80
Purchase #3	$72.39	12.484%	$81.4272	$81.43	$81.45	$81.40
Purchase #4	$67.63	5.482%	$71.3375	$71.34	$71.35	$71.30
Purchase #5	$5.86	11.230%	$6.5181	$6.52	$6.50	$6.50
Purchase #6	$217.93	7.630%	$234.5581	$234.56	$234.55	$234.60
Purchase #7	$233.89	7.213%	$250.7605	$250.76	$250.75	$250.80
7 purchase totals =	$939.89		$1,012.6456	$1,012.65	$1,012.60	$1,012.60