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	$25.53	6.540%	$27.1997	$27.20	$27.20	$27.20
Purchase #2	$50.73	8.863%	$55.2262	$55.23	$55.25	$55.20
Purchase #3	$90.47	6.821%	$96.641	$96.64	$96.65	$96.60
Purchase #4	$37.96	3.812%	$39.407	$39.41	$39.40	$39.40
Purchase #5	$196.86	6.190%	$209.0456	$209.05	$209.05	$209.00
Purchase #6	$125.37	4.748%	$131.3226	$131.32	$131.30	$131.30
Purchase #7	$91.85	8.834%	$99.964	$99.96	$99.95	$100.00
7 purchase totals =	$618.77		$658.8061	$658.81	$658.80	$658.70