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	$149.79	11.830%	$167.5102	$167.51	$167.50	$167.50
Purchase #2	$107.52	4.134%	$111.9649	$111.96	$111.95	$112.00
Purchase #3	$42.57	7.216%	$45.6419	$45.64	$45.65	$45.60
Purchase #4	$131.58	6.642%	$140.3195	$140.32	$140.30	$140.30
Purchase #5	$168.91	10.108%	$185.9834	$185.98	$186.00	$186.00
Purchase #6	$75.54	9.397%	$82.6385	$82.64	$82.65	$82.60
Purchase #7	$211.84	9.708%	$232.4054	$232.41	$232.40	$232.40
7 purchase totals =	$887.75		$966.4638	$966.46	$966.45	$966.40