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	$113.76	12.507%	$127.988	$127.99	$128.00	$128.00
Purchase #2	$182.40	8.835%	$198.515	$198.52	$198.50	$198.50
Purchase #3	$73.49	5.495%	$77.5283	$77.53	$77.55	$77.50
Purchase #4	$82.78	12.689%	$93.284	$93.28	$93.30	$93.30
Purchase #5	$117.63	8.597%	$127.7427	$127.74	$127.75	$127.70
Purchase #6	$105.69	5.263%	$111.2525	$111.25	$111.25	$111.30
Purchase #7	$167.90	8.122%	$181.5368	$181.54	$181.55	$181.50
7 purchase totals =	$843.65		$917.8473	$917.85	$917.90	$917.80