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	$87.36	3.854%	$90.7269	$90.73	$90.75	$90.70
Purchase #2	$233.73	11.622%	$260.8941	$260.89	$260.90	$260.90
Purchase #3	$162.62	3.151%	$167.7442	$167.74	$167.75	$167.70
Purchase #4	$232.88	9.194%	$254.291	$254.29	$254.30	$254.30
Purchase #5	$82.96	8.135%	$89.7088	$89.71	$89.70	$89.70
Purchase #6	$73.57	7.810%	$79.3158	$79.32	$79.30	$79.30
Purchase #7	$227.34	8.608%	$246.9094	$246.91	$246.90	$246.90
7 purchase totals =	$1,100.46		$1,189.5902	$1,189.59	$1,189.60	$1,189.50