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	$91.84	8.765%	$99.8898	$99.89	$99.90	$99.90
Purchase #2	$27.64	12.329%	$31.0477	$31.05	$31.05	$31.00
Purchase #3	$239.57	12.274%	$268.9748	$268.97	$268.95	$269.00
Purchase #4	$209.70	6.348%	$223.0118	$223.01	$223.00	$223.00
Purchase #5	$187.82	9.453%	$205.5746	$205.57	$205.55	$205.60
Purchase #6	$164.30	9.588%	$180.0531	$180.05	$180.05	$180.10
Purchase #7	$78.71	5.274%	$82.8612	$82.86	$82.85	$82.90
7 purchase totals =	$999.58		$1,091.4130	$1,091.40	$1,091.35	$1,091.50