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	$122.77	12.342%	$137.9223	$137.92	$137.90	$137.90
Purchase #2	$249.75	9.830%	$274.3004	$274.30	$274.30	$274.30
Purchase #3	$80.60	11.572%	$89.927	$89.93	$89.95	$89.90
Purchase #4	$58.63	6.438%	$62.4046	$62.40	$62.40	$62.40
Purchase #5	$227.81	6.794%	$243.2874	$243.29	$243.30	$243.30
Purchase #6	$170.77	8.441%	$185.1847	$185.18	$185.20	$185.20
Purchase #7	$185.55	13.478%	$210.5584	$210.56	$210.55	$210.60
7 purchase totals =	$1,095.88		$1,203.5848	$1,203.58	$1,203.60	$1,203.60