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	$37.82	8.325%	$40.9685	$40.97	$40.95	$41.00
Purchase #2	$241.95	11.498%	$269.7694	$269.77	$269.75	$269.80
Purchase #3	$188.54	7.850%	$203.3404	$203.34	$203.35	$203.30
Purchase #4	$54.26	7.504%	$58.3317	$58.33	$58.35	$58.30
Purchase #5	$131.61	9.431%	$144.0221	$144.02	$144.00	$144.00
Purchase #6	$80.69	12.180%	$90.518	$90.52	$90.50	$90.50
Purchase #7	$244.46	12.861%	$275.9	$275.90	$275.90	$275.90
7 purchase totals =	$979.33		$1,082.8501	$1,082.85	$1,082.80	$1,082.80