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	$7.33	8.569%	$7.9581	$7.96	$7.95	$8.00
Purchase #2	$146.33	12.248%	$164.2525	$164.25	$164.25	$164.30
Purchase #3	$47.34	13.156%	$53.5681	$53.57	$53.55	$53.60
Purchase #4	$32.97	12.333%	$37.0362	$37.04	$37.05	$37.00
Purchase #5	$40.71	3.501%	$42.1353	$42.14	$42.15	$42.10
Purchase #6	$248.83	8.126%	$269.0499	$269.05	$269.05	$269.00
Purchase #7	$61.67	3.608%	$63.8951	$63.90	$63.90	$63.90
7 purchase totals =	$585.18		$637.8952	$637.91	$637.90	$637.90