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	$80.92	3.623%	$83.8517	$83.85	$83.85	$83.90
Purchase #2	$80.72	10.367%	$89.0882	$89.09	$89.10	$89.10
Purchase #3	$29.90	6.489%	$31.8402	$31.84	$31.85	$31.80
Purchase #4	$110.32	6.412%	$117.3937	$117.39	$117.40	$117.40
Purchase #5	$42.39	12.701%	$47.774	$47.77	$47.75	$47.80
Purchase #6	$58.53	5.400%	$61.6906	$61.69	$61.70	$61.70
Purchase #7	$150.37	10.333%	$165.9077	$165.91	$165.90	$165.90
7 purchase totals =	$553.15		$597.5461	$597.54	$597.55	$597.60