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	$242.53	3.278%	$250.4801	$250.48	$250.50	$250.50
Purchase #2	$140.86	4.529%	$147.2395	$147.24	$147.25	$147.20
Purchase #3	$185.75	7.299%	$199.3079	$199.31	$199.30	$199.30
Purchase #4	$237.46	11.568%	$264.9294	$264.93	$264.95	$264.90
Purchase #5	$97.41	11.688%	$108.7953	$108.80	$108.80	$108.80
Purchase #6	$94.49	6.389%	$100.527	$100.53	$100.55	$100.50
Purchase #7	$109.27	6.666%	$116.5539	$116.55	$116.55	$116.60
7 purchase totals =	$1,107.77		$1,187.8331	$1,187.84	$1,187.90	$1,187.80