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	$164.51	13.165%	$186.1677	$186.17	$186.15	$186.20
Purchase #2	$191.66	10.306%	$211.4125	$211.41	$211.40	$211.40
Purchase #3	$114.54	11.474%	$127.6823	$127.68	$127.70	$127.70
Purchase #4	$63.33	6.514%	$67.4553	$67.46	$67.45	$67.50
Purchase #5	$116.62	7.594%	$125.4761	$125.48	$125.50	$125.50
Purchase #6	$71.52	10.646%	$79.134	$79.13	$79.15	$79.10
Purchase #7	$27.56	3.443%	$28.5089	$28.51	$28.50	$28.50
7 purchase totals =	$749.74		$825.8368	$825.84	$825.85	$825.90