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	$117.47	4.797%	$123.105	$123.11	$123.10	$123.10
Purchase #2	$208.40	9.304%	$227.7895	$227.79	$227.80	$227.80
Purchase #3	$83.35	6.317%	$88.6152	$88.62	$88.60	$88.60
Purchase #4	$125.66	12.134%	$140.9076	$140.91	$140.90	$140.90
Purchase #5	$62.33	4.660%	$65.2346	$65.23	$65.25	$65.20
Purchase #6	$72.48	5.333%	$76.3454	$76.35	$76.35	$76.30
Purchase #7	$196.47	12.200%	$220.4393	$220.44	$220.45	$220.40
7 purchase totals =	$866.16		$942.4366	$942.45	$942.45	$942.30