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	$6.46	8.741%	$7.0247	$7.02	$7.00	$7.00
Purchase #2	$68.27	7.499%	$73.3896	$73.39	$73.40	$73.40
Purchase #3	$9.60	11.643%	$10.7177	$10.72	$10.70	$10.70
Purchase #4	$234.90	3.833%	$243.9037	$243.90	$243.90	$243.90
Purchase #5	$193.81	3.171%	$199.9557	$199.96	$199.95	$200.00
Purchase #6	$85.80	4.465%	$89.631	$89.63	$89.65	$89.60
Purchase #7	$39.88	6.222%	$42.3613	$42.36	$42.35	$42.40
7 purchase totals =	$638.72		$666.9837	$666.98	$666.95	$667.00