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	$98.79	4.591%	$103.3254	$103.33	$103.35	$103.30
Purchase #2	$99.38	7.556%	$106.8892	$106.89	$106.90	$106.90
Purchase #3	$82.63	8.106%	$89.328	$89.33	$89.35	$89.30
Purchase #4	$172.64	8.141%	$186.6946	$186.69	$186.70	$186.70
Purchase #5	$186.81	5.327%	$196.7614	$196.76	$196.75	$196.80
Purchase #6	$63.98	7.223%	$68.6013	$68.60	$68.60	$68.60
Purchase #7	$242.41	11.434%	$270.1272	$270.13	$270.15	$270.10
7 purchase totals =	$946.64		$1,021.7271	$1,021.73	$1,021.80	$1,021.70