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	$121.69	7.841%	$131.2317	$131.23	$131.25	$131.20
Purchase #2	$189.62	3.406%	$196.0785	$196.08	$196.10	$196.10
Purchase #3	$83.28	11.481%	$92.8414	$92.84	$92.85	$92.80
Purchase #4	$183.33	9.564%	$200.8637	$200.86	$200.85	$200.90
Purchase #5	$169.90	7.510%	$182.6595	$182.66	$182.65	$182.70
Purchase #6	$67.35	6.634%	$71.818	$71.82	$71.80	$71.80
Purchase #7	$69.61	5.438%	$73.3954	$73.40	$73.40	$73.40
7 purchase totals =	$884.78		$948.8882	$948.89	$948.90	$948.90