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	$138.51	13.786%	$157.605	$157.61	$157.60	$157.60
Purchase #2	$85.90	12.121%	$96.3119	$96.31	$96.30	$96.30
Purchase #3	$98.53	13.229%	$111.5645	$111.56	$111.55	$111.60
Purchase #4	$73.75	11.535%	$82.2571	$82.26	$82.25	$82.30
Purchase #5	$69.83	13.428%	$79.2068	$79.21	$79.20	$79.20
Purchase #6	$93.63	11.354%	$104.2608	$104.26	$104.25	$104.30
Purchase #7	$109.94	11.505%	$122.5886	$122.59	$122.60	$122.60
7 purchase totals =	$670.09		$753.7947	$753.80	$753.75	$753.90