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	$150.71	10.540%	$166.5948	$166.59	$166.60	$166.60
Purchase #2	$78.96	8.740%	$85.8611	$85.86	$85.85	$85.90
Purchase #3	$60.48	12.288%	$67.9118	$67.91	$67.90	$67.90
Purchase #4	$206.59	8.582%	$224.3196	$224.32	$224.30	$224.30
Purchase #5	$223.83	12.470%	$251.7416	$251.74	$251.75	$251.70
Purchase #6	$147.89	4.622%	$154.7255	$154.73	$154.75	$154.70
Purchase #7	$73.87	5.678%	$78.0643	$78.06	$78.05	$78.10
7 purchase totals =	$942.33		$1,029.2187	$1,029.21	$1,029.20	$1,029.20