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	$99.45	9.343%	$108.7416	$108.74	$108.75	$108.70
Purchase #2	$142.76	8.736%	$155.2315	$155.23	$155.25	$155.20
Purchase #3	$32.96	10.779%	$36.5128	$36.51	$36.50	$36.50
Purchase #4	$143.93	7.646%	$154.9349	$154.93	$154.95	$154.90
Purchase #5	$197.86	9.119%	$215.9029	$215.90	$215.90	$215.90
Purchase #6	$96.85	13.735%	$110.1523	$110.15	$110.15	$110.20
Purchase #7	$200.25	11.300%	$222.8783	$222.88	$222.90	$222.90
7 purchase totals =	$914.06		$1,004.3543	$1,004.34	$1,004.40	$1,004.30