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	$19.53	7.192%	$20.9346	$20.93	$20.95	$20.90
Purchase #2	$248.88	12.112%	$279.0243	$279.02	$279.00	$279.00
Purchase #3	$185.55	6.130%	$196.9242	$196.92	$196.90	$196.90
Purchase #4	$151.59	3.136%	$156.3439	$156.34	$156.35	$156.30
Purchase #5	$45.61	5.140%	$47.9544	$47.95	$47.95	$48.00
Purchase #6	$218.73	8.314%	$236.9152	$236.92	$236.90	$236.90
Purchase #7	$168.59	8.503%	$182.9252	$182.93	$182.95	$182.90
7 purchase totals =	$1,038.48		$1,121.0218	$1,121.01	$1,121.00	$1,120.90