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	$213.98	13.839%	$243.5927	$243.59	$243.60	$243.60
Purchase #2	$79.96	6.389%	$85.0686	$85.07	$85.05	$85.10
Purchase #3	$156.69	4.682%	$164.0262	$164.03	$164.05	$164.00
Purchase #4	$93.60	8.736%	$101.7769	$101.78	$101.80	$101.80
Purchase #5	$99.31	7.303%	$106.5626	$106.56	$106.55	$106.60
Purchase #6	$54.95	12.700%	$61.9287	$61.93	$61.95	$61.90
Purchase #7	$209.82	8.571%	$227.8037	$227.80	$227.80	$227.80
7 purchase totals =	$908.31		$990.7594	$990.76	$990.80	$990.80