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	$5.73	6.339%	$6.0932	$6.09	$6.10	$6.10
Purchase #2	$120.86	10.494%	$133.543	$133.54	$133.55	$133.50
Purchase #3	$170.91	8.776%	$185.9091	$185.91	$185.90	$185.90
Purchase #4	$103.32	6.213%	$109.7393	$109.74	$109.75	$109.70
Purchase #5	$165.58	10.565%	$183.0735	$183.07	$183.05	$183.10
Purchase #6	$58.72	10.462%	$64.8633	$64.86	$64.85	$64.90
Purchase #7	$39.92	12.782%	$45.0226	$45.02	$45.00	$45.00
7 purchase totals =	$665.04		$728.2440	$728.23	$728.20	$728.20