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	$71.46	8.401%	$77.4634	$77.46	$77.45	$77.50
Purchase #2	$219.66	10.781%	$243.3415	$243.34	$243.35	$243.30
Purchase #3	$137.38	13.521%	$155.9551	$155.96	$155.95	$156.00
Purchase #4	$131.87	3.513%	$136.5026	$136.50	$136.50	$136.50
Purchase #5	$126.76	6.510%	$135.0121	$135.01	$135.00	$135.00
Purchase #6	$150.84	10.465%	$166.6254	$166.63	$166.65	$166.60
Purchase #7	$85.54	4.680%	$89.5433	$89.54	$89.55	$89.50
7 purchase totals =	$923.51		$1,004.4434	$1,004.44	$1,004.45	$1,004.40