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	$37.67	12.165%	$42.2526	$42.25	$42.25	$42.30
Purchase #2	$52.39	13.460%	$59.4417	$59.44	$59.45	$59.40
Purchase #3	$39.62	8.631%	$43.0396	$43.04	$43.05	$43.00
Purchase #4	$208.55	9.283%	$227.9097	$227.91	$227.90	$227.90
Purchase #5	$149.73	13.400%	$169.7938	$169.79	$169.80	$169.80
Purchase #6	$35.25	4.486%	$36.8313	$36.83	$36.85	$36.80
Purchase #7	$187.53	3.573%	$194.2304	$194.23	$194.25	$194.20
7 purchase totals =	$710.74		$773.4991	$773.49	$773.55	$773.40