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	$18.49	9.538%	$20.2536	$20.25	$20.25	$20.30
Purchase #2	$77.72	5.805%	$82.2316	$82.23	$82.25	$82.20
Purchase #3	$19.76	10.148%	$21.7652	$21.77	$21.75	$21.80
Purchase #4	$136.65	11.334%	$152.1379	$152.14	$152.15	$152.10
Purchase #5	$225.50	5.683%	$238.3152	$238.32	$238.30	$238.30
Purchase #6	$185.57	7.736%	$199.9257	$199.93	$199.95	$199.90
Purchase #7	$181.98	13.328%	$206.2343	$206.23	$206.25	$206.20
7 purchase totals =	$845.67		$920.8635	$920.87	$920.90	$920.80