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	$81.68	9.758%	$89.6503	$89.65	$89.65	$89.70
Purchase #2	$209.48	3.460%	$216.728	$216.73	$216.75	$216.70
Purchase #3	$88.53	12.440%	$99.5431	$99.54	$99.55	$99.50
Purchase #4	$207.50	10.304%	$228.8808	$228.88	$228.90	$228.90
Purchase #5	$249.81	11.576%	$278.728	$278.73	$278.75	$278.70
Purchase #6	$221.70	3.539%	$229.546	$229.55	$229.55	$229.50
Purchase #7	$33.97	6.746%	$36.2616	$36.26	$36.25	$36.30
7 purchase totals =	$1,092.67		$1,179.3378	$1,179.34	$1,179.40	$1,179.30