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	$60.34	13.270%	$68.3471	$68.35	$68.35	$68.30
Purchase #2	$156.39	12.412%	$175.8011	$175.80	$175.80	$175.80
Purchase #3	$71.76	8.432%	$77.8108	$77.81	$77.80	$77.80
Purchase #4	$11.86	8.600%	$12.88	$12.88	$12.90	$12.90
Purchase #5	$133.55	12.702%	$150.5135	$150.51	$150.50	$150.50
Purchase #6	$42.72	7.129%	$45.7655	$45.77	$45.75	$45.80
Purchase #7	$85.38	4.736%	$89.4236	$89.42	$89.40	$89.40
7 purchase totals =	$562.00		$620.5416	$620.54	$620.50	$620.50