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	$88.57	12.370%	$99.5261	$99.53	$99.55	$99.50
Purchase #2	$158.75	6.479%	$169.0354	$169.04	$169.05	$169.00
Purchase #3	$240.51	10.229%	$265.1118	$265.11	$265.10	$265.10
Purchase #4	$142.86	8.396%	$154.8545	$154.85	$154.85	$154.90
Purchase #5	$116.81	6.147%	$123.9903	$123.99	$124.00	$124.00
Purchase #6	$110.45	3.235%	$114.0231	$114.02	$114.00	$114.00
Purchase #7	$152.50	7.831%	$164.4423	$164.44	$164.45	$164.40
7 purchase totals =	$1,010.45		$1,090.9835	$1,090.98	$1,091.00	$1,090.90