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	$37.98	13.168%	$42.9812	$42.98	$43.00	$43.00
Purchase #2	$102.48	6.682%	$109.3277	$109.33	$109.35	$109.30
Purchase #3	$168.76	5.769%	$178.4958	$178.50	$178.50	$178.50
Purchase #4	$85.49	4.767%	$89.5653	$89.57	$89.55	$89.60
Purchase #5	$114.73	4.787%	$120.2221	$120.22	$120.20	$120.20
Purchase #6	$91.46	7.110%	$97.9628	$97.96	$97.95	$98.00
Purchase #7	$20.51	5.558%	$21.6499	$21.65	$21.65	$21.60
7 purchase totals =	$621.41		$660.2048	$660.21	$660.20	$660.20