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	$75.82	9.310%	$82.8788	$82.88	$82.90	$82.90
Purchase #2	$85.61	3.686%	$88.7656	$88.77	$88.75	$88.80
Purchase #3	$250.87	10.502%	$277.2164	$277.22	$277.20	$277.20
Purchase #4	$242.34	3.421%	$250.6305	$250.63	$250.65	$250.60
Purchase #5	$232.88	7.507%	$250.3623	$250.36	$250.35	$250.40
Purchase #6	$39.50	10.589%	$43.6827	$43.68	$43.70	$43.70
Purchase #7	$200.56	9.148%	$218.9072	$218.91	$218.90	$218.90
7 purchase totals =	$1,127.58		$1,212.4435	$1,212.45	$1,212.45	$1,212.50