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	$178.35	6.557%	$190.0444	$190.04	$190.05	$190.00
Purchase #2	$80.87	5.517%	$85.3316	$85.33	$85.35	$85.30
Purchase #3	$194.77	7.849%	$210.0575	$210.06	$210.05	$210.10
Purchase #4	$31.86	7.825%	$34.353	$34.35	$34.35	$34.40
Purchase #5	$203.61	9.523%	$222.9998	$223.00	$223.00	$223.00
Purchase #6	$90.54	10.459%	$100.0096	$100.01	$100.00	$100.00
Purchase #7	$164.51	6.507%	$175.2147	$175.21	$175.20	$175.20
7 purchase totals =	$944.51		$1,018.0106	$1,018.00	$1,018.00	$1,018.00