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	$223.78	12.106%	$250.8708	$250.87	$250.85	$250.90
Purchase #2	$83.47	4.873%	$87.5375	$87.54	$87.55	$87.50
Purchase #3	$66.58	4.103%	$69.3118	$69.31	$69.30	$69.30
Purchase #4	$227.57	8.503%	$246.9203	$246.92	$246.90	$246.90
Purchase #5	$35.30	5.840%	$37.3615	$37.36	$37.35	$37.40
Purchase #6	$242.74	10.504%	$268.2374	$268.24	$268.25	$268.20
Purchase #7	$39.28	7.794%	$42.3415	$42.34	$42.35	$42.30
7 purchase totals =	$918.72		$1,002.5808	$1,002.58	$1,002.55	$1,002.50