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	$10.63	11.346%	$11.8361	$11.84	$11.85	$11.80
Purchase #2	$186.43	12.198%	$209.1707	$209.17	$209.15	$209.20
Purchase #3	$179.61	8.427%	$194.7457	$194.75	$194.75	$194.70
Purchase #4	$215.56	12.765%	$243.0762	$243.08	$243.10	$243.10
Purchase #5	$96.90	3.336%	$100.1326	$100.13	$100.15	$100.10
Purchase #6	$81.79	9.387%	$89.4676	$89.47	$89.45	$89.50
Purchase #7	$175.62	9.267%	$191.8947	$191.89	$191.90	$191.90
7 purchase totals =	$946.54		$1,040.3236	$1,040.33	$1,040.35	$1,040.30