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	$170.66	10.381%	$188.3762	$188.38	$188.40	$188.40
Purchase #2	$213.46	4.666%	$223.42	$223.42	$223.40	$223.40
Purchase #3	$6.34	8.775%	$6.8963	$6.90	$6.90	$6.90
Purchase #4	$49.96	7.742%	$53.8279	$53.83	$53.85	$53.80
Purchase #5	$36.73	12.483%	$41.315	$41.32	$41.30	$41.30
Purchase #6	$122.46	7.711%	$131.9029	$131.90	$131.90	$131.90
Purchase #7	$189.74	7.109%	$203.2286	$203.23	$203.25	$203.20
7 purchase totals =	$789.35		$848.9669	$848.98	$849.00	$848.90