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	$125.33	4.817%	$131.3671	$131.37	$131.35	$131.40
Purchase #2	$90.31	4.300%	$94.1933	$94.19	$94.20	$94.20
Purchase #3	$66.53	9.418%	$72.7958	$72.80	$72.80	$72.80
Purchase #4	$73.84	10.794%	$81.8103	$81.81	$81.80	$81.80
Purchase #5	$16.34	13.140%	$18.4871	$18.49	$18.50	$18.50
Purchase #6	$66.26	9.269%	$72.4016	$72.40	$72.40	$72.40
Purchase #7	$75.31	5.553%	$79.492	$79.49	$79.50	$79.50
7 purchase totals =	$513.92		$550.5472	$550.55	$550.55	$550.60