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	$167.40	10.766%	$185.4223	$185.42	$185.40	$185.40
Purchase #2	$125.78	4.157%	$131.0087	$131.01	$131.00	$131.00
Purchase #3	$60.76	6.782%	$64.8807	$64.88	$64.90	$64.90
Purchase #4	$137.46	3.170%	$141.8175	$141.82	$141.80	$141.80
Purchase #5	$31.69	8.828%	$34.4876	$34.49	$34.50	$34.50
Purchase #6	$72.38	3.726%	$75.0769	$75.08	$75.10	$75.10
Purchase #7	$196.41	6.819%	$209.8032	$209.80	$209.80	$209.80
7 purchase totals =	$791.88		$842.4969	$842.50	$842.50	$842.50