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	$227.45	12.162%	$255.1125	$255.11	$255.10	$255.10
Purchase #2	$174.50	3.635%	$180.8431	$180.84	$180.85	$180.80
Purchase #3	$115.33	11.334%	$128.4015	$128.40	$128.40	$128.40
Purchase #4	$67.70	7.539%	$72.8039	$72.80	$72.80	$72.80
Purchase #5	$29.84	13.562%	$33.8869	$33.89	$33.90	$33.90
Purchase #6	$121.59	13.365%	$137.8405	$137.84	$137.85	$137.80
Purchase #7	$114.87	3.299%	$118.6596	$118.66	$118.65	$118.70
7 purchase totals =	$851.28		$927.5480	$927.54	$927.55	$927.50