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	$28.87	8.731%	$31.3906	$31.39	$31.40	$31.40
Purchase #2	$81.96	9.118%	$89.4331	$89.43	$89.45	$89.40
Purchase #3	$210.71	13.394%	$238.9325	$238.93	$238.95	$238.90
Purchase #4	$11.63	4.783%	$12.1863	$12.19	$12.20	$12.20
Purchase #5	$180.35	10.487%	$199.2633	$199.26	$199.25	$199.30
Purchase #6	$29.98	9.802%	$32.9186	$32.92	$32.90	$32.90
Purchase #7	$66.74	9.868%	$73.3259	$73.33	$73.35	$73.30
7 purchase totals =	$610.24		$677.4503	$677.45	$677.50	$677.40