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	$36.93	9.419%	$40.4084	$40.41	$40.40	$40.40
Purchase #2	$42.76	10.688%	$47.3302	$47.33	$47.35	$47.30
Purchase #3	$175.54	6.141%	$186.3199	$186.32	$186.30	$186.30
Purchase #4	$64.72	5.571%	$68.3256	$68.33	$68.35	$68.30
Purchase #5	$7.40	6.790%	$7.9025	$7.90	$7.90	$7.90
Purchase #6	$117.52	9.200%	$128.3318	$128.33	$128.35	$128.30
Purchase #7	$67.77	7.382%	$72.7728	$72.77	$72.75	$72.80
7 purchase totals =	$512.64		$551.3912	$551.39	$551.40	$551.30