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	$56.31	6.290%	$59.8519	$59.85	$59.85	$59.90
Purchase #2	$212.85	6.255%	$226.1638	$226.16	$226.15	$226.20
Purchase #3	$243.36	11.314%	$270.8938	$270.89	$270.90	$270.90
Purchase #4	$70.70	10.379%	$78.038	$78.04	$78.05	$78.00
Purchase #5	$61.41	12.546%	$69.1145	$69.11	$69.10	$69.10
Purchase #6	$246.72	9.519%	$270.2053	$270.21	$270.20	$270.20
Purchase #7	$117.67	6.681%	$125.5315	$125.53	$125.55	$125.50
7 purchase totals =	$1,009.02		$1,099.7988	$1,099.79	$1,099.80	$1,099.80