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	$67.85	6.148%	$72.0214	$72.02	$72.00	$72.00
Purchase #2	$162.39	12.203%	$182.2065	$182.21	$182.20	$182.20
Purchase #3	$181.59	3.696%	$188.3016	$188.30	$188.30	$188.30
Purchase #4	$52.56	13.606%	$59.7113	$59.71	$59.70	$59.70
Purchase #5	$162.29	13.290%	$183.8583	$183.86	$183.85	$183.90
Purchase #6	$107.83	5.626%	$113.8965	$113.90	$113.90	$113.90
Purchase #7	$103.41	9.588%	$113.325	$113.33	$113.35	$113.30
7 purchase totals =	$837.92		$913.3206	$913.33	$913.30	$913.30