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	$37.46	12.786%	$42.2496	$42.25	$42.25	$42.20
Purchase #2	$206.62	5.842%	$218.6907	$218.69	$218.70	$218.70
Purchase #3	$133.73	13.507%	$151.7929	$151.79	$151.80	$151.80
Purchase #4	$135.33	11.844%	$151.3585	$151.36	$151.35	$151.40
Purchase #5	$73.44	11.851%	$82.1434	$82.14	$82.15	$82.10
Purchase #6	$44.45	11.850%	$49.7173	$49.72	$49.70	$49.70
Purchase #7	$84.51	7.426%	$90.7857	$90.79	$90.80	$90.80
7 purchase totals =	$715.54		$786.7381	$786.74	$786.75	$786.70