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	$51.32	12.810%	$57.8941	$57.89	$57.90	$57.90
Purchase #2	$174.94	9.778%	$192.0456	$192.05	$192.05	$192.00
Purchase #3	$138.98	11.558%	$155.0433	$155.04	$155.05	$155.00
Purchase #4	$168.48	9.540%	$184.553	$184.55	$184.55	$184.60
Purchase #5	$175.96	8.788%	$191.4234	$191.42	$191.40	$191.40
Purchase #6	$152.77	4.208%	$159.1986	$159.20	$159.20	$159.20
Purchase #7	$147.79	3.148%	$152.4424	$152.44	$152.45	$152.40
7 purchase totals =	$1,010.24		$1,092.6004	$1,092.59	$1,092.60	$1,092.50