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	$53.85	7.360%	$57.8134	$57.81	$57.80	$57.80
Purchase #2	$211.26	9.476%	$231.279	$231.28	$231.30	$231.30
Purchase #3	$37.47	12.666%	$42.216	$42.22	$42.20	$42.20
Purchase #4	$175.50	8.740%	$190.8387	$190.84	$190.85	$190.80
Purchase #5	$89.50	8.281%	$96.9115	$96.91	$96.90	$96.90
Purchase #6	$201.56	13.378%	$228.5247	$228.52	$228.50	$228.50
Purchase #7	$236.37	13.654%	$268.644	$268.64	$268.65	$268.60
7 purchase totals =	$1,005.51		$1,116.2273	$1,116.22	$1,116.20	$1,116.10