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	$49.70	6.329%	$52.8455	$52.85	$52.85	$52.80
Purchase #2	$25.46	8.533%	$27.6325	$27.63	$27.65	$27.60
Purchase #3	$109.90	5.580%	$116.0324	$116.03	$116.05	$116.00
Purchase #4	$209.83	6.579%	$223.6347	$223.63	$223.65	$223.60
Purchase #5	$36.70	8.617%	$39.8624	$39.86	$39.85	$39.90
Purchase #6	$89.35	6.701%	$95.3373	$95.34	$95.35	$95.30
Purchase #7	$237.37	13.280%	$268.8927	$268.89	$268.90	$268.90
7 purchase totals =	$758.31		$824.2375	$824.23	$824.30	$824.10