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	$71.88	9.712%	$78.861	$78.86	$78.85	$78.90
Purchase #2	$73.66	12.874%	$83.143	$83.14	$83.15	$83.10
Purchase #3	$135.54	7.163%	$145.2487	$145.25	$145.25	$145.20
Purchase #4	$211.73	13.336%	$239.9663	$239.97	$239.95	$240.00
Purchase #5	$160.73	4.229%	$167.5273	$167.53	$167.55	$167.50
Purchase #6	$91.69	8.790%	$99.7496	$99.75	$99.75	$99.70
Purchase #7	$79.44	7.453%	$85.3607	$85.36	$85.35	$85.40
7 purchase totals =	$824.67		$899.8566	$899.86	$899.85	$899.80