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	$45.30	10.869%	$50.2237	$50.22	$50.20	$50.20
Purchase #2	$211.36	5.208%	$222.3676	$222.37	$222.35	$222.40
Purchase #3	$116.38	3.639%	$120.6151	$120.62	$120.60	$120.60
Purchase #4	$32.31	9.586%	$35.4072	$35.41	$35.40	$35.40
Purchase #5	$147.71	7.811%	$159.2476	$159.25	$159.25	$159.20
Purchase #6	$69.54	12.632%	$78.3243	$78.32	$78.30	$78.30
Purchase #7	$162.89	4.236%	$169.79	$169.79	$169.80	$169.80
7 purchase totals =	$785.49		$835.9755	$835.98	$835.90	$835.90