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	$49.54	4.720%	$51.8783	$51.88	$51.90	$51.90
Purchase #2	$209.56	12.798%	$236.3795	$236.38	$236.40	$236.40
Purchase #3	$130.38	10.811%	$144.4754	$144.48	$144.50	$144.50
Purchase #4	$185.90	13.426%	$210.8589	$210.86	$210.85	$210.90
Purchase #5	$213.26	8.568%	$231.5321	$231.53	$231.55	$231.50
Purchase #6	$142.36	10.122%	$156.7697	$156.77	$156.75	$156.80
Purchase #7	$75.81	4.736%	$79.4004	$79.40	$79.40	$79.40
7 purchase totals =	$1,006.81		$1,111.2943	$1,111.30	$1,111.35	$1,111.40