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	$70.27	12.132%	$78.7952	$78.80	$78.80	$78.80
Purchase #2	$96.70	12.804%	$109.0815	$109.08	$109.10	$109.10
Purchase #3	$38.27	4.116%	$39.8452	$39.85	$39.85	$39.80
Purchase #4	$135.81	13.471%	$154.105	$154.11	$154.10	$154.10
Purchase #5	$202.62	13.213%	$229.3922	$229.39	$229.40	$229.40
Purchase #6	$25.85	11.630%	$28.8564	$28.86	$28.85	$28.90
Purchase #7	$148.48	13.524%	$168.5604	$168.56	$168.55	$168.60
7 purchase totals =	$718.00		$808.6359	$808.65	$808.65	$808.70