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	$83.37	7.607%	$89.712	$89.71	$89.70	$89.70
Purchase #2	$237.97	12.121%	$266.8143	$266.81	$266.80	$266.80
Purchase #3	$181.83	9.223%	$198.6002	$198.60	$198.60	$198.60
Purchase #4	$53.79	6.690%	$57.3886	$57.39	$57.40	$57.40
Purchase #5	$243.48	11.270%	$270.9202	$270.92	$270.90	$270.90
Purchase #6	$76.32	12.579%	$85.9203	$85.92	$85.90	$85.90
Purchase #7	$100.29	10.462%	$110.7823	$110.78	$110.80	$110.80
7 purchase totals =	$977.05		$1,080.1379	$1,080.13	$1,080.10	$1,080.10