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	$28.36	9.714%	$31.1149	$31.11	$31.10	$31.10
Purchase #2	$62.33	10.525%	$68.8902	$68.89	$68.90	$68.90
Purchase #3	$176.88	7.703%	$190.5051	$190.51	$190.50	$190.50
Purchase #4	$223.85	9.686%	$245.5321	$245.53	$245.55	$245.50
Purchase #5	$127.74	11.561%	$142.508	$142.51	$142.50	$142.50
Purchase #6	$220.85	9.710%	$242.2945	$242.29	$242.30	$242.30
Purchase #7	$57.48	7.663%	$61.8847	$61.88	$61.90	$61.90
7 purchase totals =	$897.49		$982.7295	$982.72	$982.75	$982.70