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	$32.71	11.668%	$36.5266	$36.53	$36.55	$36.50
Purchase #2	$166.46	9.266%	$181.8842	$181.88	$181.90	$181.90
Purchase #3	$102.80	5.359%	$108.3091	$108.31	$108.30	$108.30
Purchase #4	$90.33	9.165%	$98.6087	$98.61	$98.60	$98.60
Purchase #5	$28.61	13.858%	$32.5748	$32.57	$32.55	$32.60
Purchase #6	$63.26	6.556%	$67.4073	$67.41	$67.40	$67.40
Purchase #7	$36.66	4.666%	$38.3706	$38.37	$38.35	$38.40
7 purchase totals =	$520.83		$563.6813	$563.68	$563.65	$563.70