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	$78.47	3.109%	$80.9096	$80.91	$80.90	$80.90
Purchase #2	$141.90	7.691%	$152.8135	$152.81	$152.80	$152.80
Purchase #3	$167.66	11.372%	$186.7263	$186.73	$186.75	$186.70
Purchase #4	$23.72	11.259%	$26.3906	$26.39	$26.40	$26.40
Purchase #5	$150.33	3.308%	$155.3029	$155.30	$155.30	$155.30
Purchase #6	$84.34	7.532%	$90.6925	$90.69	$90.70	$90.70
Purchase #7	$199.96	3.290%	$206.5387	$206.54	$206.55	$206.50
7 purchase totals =	$846.38		$899.3741	$899.37	$899.40	$899.30