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	$96.70	4.712%	$101.2565	$101.26	$101.25	$101.30
Purchase #2	$217.81	6.219%	$231.3556	$231.36	$231.35	$231.40
Purchase #3	$83.83	6.470%	$89.2538	$89.25	$89.25	$89.30
Purchase #4	$85.69	4.252%	$89.3335	$89.33	$89.35	$89.30
Purchase #5	$71.83	8.496%	$77.9327	$77.93	$77.95	$77.90
Purchase #6	$33.40	12.271%	$37.4985	$37.50	$37.50	$37.50
Purchase #7	$240.89	8.454%	$261.2548	$261.25	$261.25	$261.30
7 purchase totals =	$830.15		$887.8854	$887.88	$887.90	$888.00