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	$199.44	5.454%	$210.3175	$210.32	$210.30	$210.30
Purchase #2	$152.73	10.628%	$168.9621	$168.96	$168.95	$169.00
Purchase #3	$226.47	7.805%	$244.146	$244.15	$244.15	$244.10
Purchase #4	$45.25	10.523%	$50.0117	$50.01	$50.00	$50.00
Purchase #5	$178.91	3.661%	$185.4599	$185.46	$185.45	$185.50
Purchase #6	$225.39	5.658%	$238.1426	$238.14	$238.15	$238.10
Purchase #7	$84.58	5.278%	$89.0441	$89.04	$89.05	$89.00
7 purchase totals =	$1,112.77		$1,186.0839	$1,186.08	$1,186.05	$1,186.00