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	$73.78	6.444%	$78.5344	$78.53	$78.55	$78.50
Purchase #2	$63.41	12.306%	$71.2132	$71.21	$71.20	$71.20
Purchase #3	$186.44	3.769%	$193.4669	$193.47	$193.45	$193.50
Purchase #4	$167.76	8.580%	$182.1538	$182.15	$182.15	$182.20
Purchase #5	$165.86	11.204%	$184.443	$184.44	$184.45	$184.40
Purchase #6	$219.36	7.386%	$235.5619	$235.56	$235.55	$235.60
Purchase #7	$144.26	5.738%	$152.5376	$152.54	$152.55	$152.50
7 purchase totals =	$1,020.87		$1,097.9108	$1,097.90	$1,097.90	$1,097.90