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	$203.34	10.322%	$224.3288	$224.33	$224.35	$224.30
Purchase #2	$32.65	9.830%	$35.8595	$35.86	$35.85	$35.90
Purchase #3	$196.88	7.304%	$211.2601	$211.26	$211.25	$211.30
Purchase #4	$103.94	11.444%	$115.8349	$115.83	$115.85	$115.80
Purchase #5	$35.26	5.381%	$37.1573	$37.16	$37.15	$37.20
Purchase #6	$143.54	5.812%	$151.8825	$151.88	$151.90	$151.90
Purchase #7	$53.84	8.574%	$58.4562	$58.46	$58.45	$58.50
7 purchase totals =	$769.45		$834.7793	$834.78	$834.80	$834.90