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	$42.25	5.625%	$44.6266	$44.63	$44.65	$44.60
Purchase #2	$185.79	7.445%	$199.6221	$199.62	$199.60	$199.60
Purchase #3	$98.43	3.428%	$101.8042	$101.80	$101.80	$101.80
Purchase #4	$131.47	4.828%	$137.8174	$137.82	$137.80	$137.80
Purchase #5	$239.46	4.545%	$250.3435	$250.34	$250.35	$250.30
Purchase #6	$168.31	13.864%	$191.6445	$191.64	$191.65	$191.60
Purchase #7	$160.69	8.713%	$174.6909	$174.69	$174.70	$174.70
7 purchase totals =	$1,026.40		$1,100.5492	$1,100.54	$1,100.55	$1,100.40