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	$39.82	3.871%	$41.3614	$41.36	$41.35	$41.40
Purchase #2	$242.56	9.206%	$264.8901	$264.89	$264.90	$264.90
Purchase #3	$123.53	12.743%	$139.2714	$139.27	$139.25	$139.30
Purchase #4	$110.90	10.576%	$122.6288	$122.63	$122.65	$122.60
Purchase #5	$137.33	10.221%	$151.3665	$151.37	$151.35	$151.40
Purchase #6	$179.29	5.362%	$188.9035	$188.90	$188.90	$188.90
Purchase #7	$108.81	8.736%	$118.3156	$118.32	$118.30	$118.30
7 purchase totals =	$942.24		$1,026.7373	$1,026.74	$1,026.70	$1,026.80