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	$89.33	10.285%	$98.5176	$98.52	$98.50	$98.50
Purchase #2	$227.56	4.124%	$236.9446	$236.94	$236.95	$236.90
Purchase #3	$82.86	10.482%	$91.5454	$91.55	$91.55	$91.50
Purchase #4	$139.96	4.753%	$146.6123	$146.61	$146.60	$146.60
Purchase #5	$164.30	7.704%	$176.9577	$176.96	$176.95	$177.00
Purchase #6	$105.79	4.366%	$110.4088	$110.41	$110.40	$110.40
Purchase #7	$70.25	12.372%	$78.9413	$78.94	$78.95	$78.90
7 purchase totals =	$880.05		$939.9277	$939.93	$939.90	$939.80