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	$80.53	10.582%	$89.0517	$89.05	$89.05	$89.10
Purchase #2	$193.41	10.542%	$213.7993	$213.80	$213.80	$213.80
Purchase #3	$201.84	10.409%	$222.8495	$222.85	$222.85	$222.80
Purchase #4	$25.75	8.366%	$27.9042	$27.90	$27.90	$27.90
Purchase #5	$114.54	5.541%	$120.8867	$120.89	$120.90	$120.90
Purchase #6	$91.43	12.867%	$103.1943	$103.19	$103.20	$103.20
Purchase #7	$59.30	4.222%	$61.8036	$61.80	$61.80	$61.80
7 purchase totals =	$766.80		$839.4893	$839.48	$839.50	$839.50