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	$79.92	11.677%	$89.2523	$89.25	$89.25	$89.30
Purchase #2	$68.89	13.717%	$78.3396	$78.34	$78.35	$78.30
Purchase #3	$78.40	11.749%	$87.6112	$87.61	$87.60	$87.60
Purchase #4	$202.34	7.789%	$218.1003	$218.10	$218.10	$218.10
Purchase #5	$155.74	7.401%	$167.2663	$167.27	$167.25	$167.30
Purchase #6	$171.73	11.874%	$192.1212	$192.12	$192.10	$192.10
Purchase #7	$75.44	13.824%	$85.8688	$85.87	$85.85	$85.90
7 purchase totals =	$832.46		$918.5597	$918.56	$918.50	$918.60